Marijuana Use Shows Significant Brain Change (UPDATED)

  • (Above) Michael Medved touched on Lady Gaga’s (Stefani Joanne Angelina Germanotta) astute and candid admissions about her addiction to marijuana. In this revealing discussion, she weaves a tale that has led her to a sober (more sober?) life. I give her props and pray she is not part of “Club Twenty-Seven.” More importantly, I hope she finds the Life Medved mentions (as I wish for Michael as well).

…Both subtle and acute changes in emotional and intellectual de­velopment occur in young marijuana users because the arc of their brain’s structural development becomes recalibrated by marijuana use. Brain researchers documented in 2008 how chronic marijuana use starting in adolescence significantly decreases the size of two brain areas thick in cannabinoid receptors—the amygdala by 7 per­cent and the hippocampus by 12 percent….

….The study found that using marijua­na regularly before age eighteen resulted in an average IQ of six to eight fewer points at age thirty-eight relative to those who did not use marijuana before age eighteen. This astounding finding was still true for those teens who used marijuana regularly but stopped us­ing the drug after the age of eighteen…..

For ex­ample, a 2007 review in Lancet compared results from thirty-five studies evaluating the impact of marijuana use on the later develop­ment of psychosis, which was defined as delusions, hallucinations, or thought disorders….

(Kevin Sabet — see below)

See my previous large post in which this accentuates: “Even Casual Marijuana Use Shows Significant Brain Change

In “Reefer Sanity“, Dr. Kevin Sabet considers the consequences of marijuana legalization. He uses a plethora of research — drawn from his almost two decades of work and policymaking in this area — to argue that the United States should not legalize marijuana with all of its attendant social costs, nor damage the future of marijuana smokers by prosecuting and jailing them. Rather, he contends we should shift our emphasis to education about the newly revealed health dangers of marijuana use, as well as focus on intervention and treatment. In short, he argues for trying these evidence-based reforms first.

(Via The Foundry) Marijuana legalization poses a significant health risk to America’s youth—and many parents have no clue about the consequences, says a former Obama administration drug policy adviser.

“Today’s marijuana is not the marijuana of the ‘60s, ‘70s or ‘80s. It’s five to 15 times stronger,” Kevin Sabet said in an exclusive interview with The Foundry. “I think a lot of Baby Boomers’ experience with pot—a couple of times in the dorm room—they don’t correspond to what kids are experiencing today.”

Sabet, a former senior adviser at the White House Office of National Drug Control Policy, wrote the book “Reefer Sanity: Seven Great Myths About Marijuana” to shed light on the marijuana legalization movement.

He pointed to Colorado, which has operated with de-facto legalization for five years, as a case study. By 2011, Denver had more medical marijuana shops than Starbucks or McDonalds.

The state has more kids using marijuana, he said, resulting in more kids in treatment and higher rate of car crashes. There have even been two deaths tied to marijuana use, including one involving domestic violence.

“Legalization in practice is a lot scarier than legalization in theory,” Sabet said. “It means a pot shop in your backyard, mass advertising and commercialization and greater health harms.”

In the book, Sabet takes on the myth that marijuana isn’t addictive. He said one in six kids who try marijuana will become addicted—the same as alcohol. That’s because young people are vulnerable than adults.

“There are more kids in treatment for marijuana today than all other drugs, including alcohol, combined,” Sabet said.

This is an excerpt from Kevin Sabat’s book, Reefer Sanity — I excluded his references to the studies, I suggest purchasing the book as it is very readable (especially if you are parents):


How marijuana became such a public health concern starts with the economic pressures felt by the drug’s growers to increase the potency of marijuana in order to raise prices—and therefore prof-its—from its sale. By constantly experimenting with breeding prac­tices and cultivation techniques over several decades, producers and growers steadily made progress in greatly elevating the levels of THC (the psychoactive ingredient) found in the oily resin of the marijuana plant’s leaves and flowers.

At the University of Mississippi, a potency-monitoring project has been under way for the past few decades, measuring the con­centration of THC in thousands of marijuana samples randomly se­lected from law-enforcement seizures. Since 1983, when THC con­centrations averaged below 4 percent, potency has intensified until it now exceeds an average of 10 percent. Many marijuana samples are in the 10-20 percent range. Some marijuana samples show THC concentrations exceeding 30 percent. If we were talking about alco­hol, this increase in intoxication potential would be like going from drinking a “lite” beer a day to consuming a dozen shots of vodka.

One obvious direct result of this intensified marijuana potency has been an even greater corresponding escalation in emergency room admissions for marijuana-related reactions. The nationwide total went from an estimated 16,251 emergency room visits in the United States related to marijuana use in 1991, to exceeding 374,000 emergency room admissions in 2008—a nearly twenty-five-fold increase in just seventeen years.

Sabet graph 1

Interestingly, the num­ber of users of marijuana stayed about the same during this period—suggesting that the increase in ER visits did not have to do simply with increased numbers of users. These reactions ranged from anxiety and panic attacks, paranoia, and psychotic symptoms, to respiratory and cardiovascular distress. An analysis of two large national surveys of marijuana addiction found that “more adults in the United States had a marijuana use disorder in 2001-2002 than in 1991-1992,” with the highest rates among young black men and women, and young Hispanic men, even though use rates were the same for the two ranges of years studied.

Today’s typical marijuana sample contains up to five-hundred chemical constituents. About seventy of these chemicals are known as cannabinoids, and one of them—THC—is psychoactive.

Human brains contain a system of cannabinoid receptors, sort of like a bleacher full of open baseball mitts available to receive pitched baseballs in the form of cannabinoid molecules. The highest concentration of these receptors is in those parts of the brain that affect thinking, memory, concentration, sensory and time percep­tion, and the coordination of body movements.

Once these brain receptors have been triggered by marijuana’s cannabinoids, which effectively begin to mimic and then hijack some brain neurotransmitters, the resulting intoxication distorts the brain’s natural chemical balance and produces distortions in thinking, problem-solving, memory, and learning, along with im­paired coordination and perceptual abilities.



As children’s brain development is disrupted by chronic marijuana use, their risk for dependency accelerates. And given the ever-in­creasing potency, marijuana becomes an expensive public health hazard with long-lasting effects.

We can measure the impact on life development from mari­juana use and its alterations of brain function in several different ways. Research shows that adolescents who smoke marijuana ev­ery weekend over a two-year period are nearly six times more like­ly to drop out of school than nonsmokers, more than three times less likely to enter college than nonsmokers, and more than four times less likely to earn a college degree. We don’t know whether marijuana causes adolescents to drop out of school or not, but given marijuana’s effect on learning and motivation, it is safe to say that marijuana use very likely has something to do with it.

Stunted emotional development is also strongly associated with adolescent marijuana use. Females show a greater vulnerability than males to this heightened risk of anxiety attacks and depression.

A 2002 study in the British Medical Journal, for instance, de­scribed how researchers in Australia studied 1,601 students aged fourteen to fifteen over a seven-year period; 60 percent had used marijuana by twenty years of age. The conclusions reached by the authors should give all parents cause for concern. They wrote: “Dai­ly use in young women was associated with an over fivefold increase in the odds of reporting a state of depression and anxiety…weekly or more frequent cannabis use in teenagers predicted an approxi­mately twofold increase in risk for later depression and anxiety.”

In order to assess a young person’s ability to perceive, un­derstand, and manage their emotions while under the influence of marijuana, a team of researchers in 2006 used a sophisticated mood-testing scale to measure emotional responses in 133 college students (114 women and 19 men) with an average age of twenty-one years. Those who had started consuming marijuana at earlier ages were found to have an impaired ability to experience normal emotional responses.

Both subtle and acute changes in emotional and intellectual de­velopment occur in young marijuana users because the arc of their brain’s structural development becomes recalibrated by marijuana use. Brain researchers documented in 2008 how chronic marijuana use starting in adolescence significantly decreases the size of two brain areas thick in cannabinoid receptors—the amygdala by 7 per­cent and the hippocampus by 12 percent. One result was that young chronic marijuana users performed much worse than nonusers on verbal learning tests. Heavy marijuana use “exerts harmful effects on brain tissue and mental health,” the authors concluded in the Ar­chives of General Psychiatry in 2008.

Memory impairment poses a serious consequence of chronic or long-term use of marijuana, and these effects can be experienced long after marijuana use is suspended. Three studies in particular make a compelling case that the “dumbing down” effect of marijua­na use extends to memory skills.

Difficulties in verbal story memory, along with impairments in learning and working memory for up to six weeks after cessation of marijuana use, were found in a review of studies published in Current Drug Abuse Reviews in 2008. These studies were of both adolescent humans and animals. Though adolescents were more adversely affected by heavy use than adults, adults who began using marijuana in adolescence “showed greater [memory] dysfunction than those who began use later.”

Another 2008 review of the medical literature determined that the evidence points overwhelmingly to “impaired encoding, stor­age, manipulation, and retrieval mechanisms [in the brains] of long­term or heavy cannabis users.”

One of the pioneering studies on marijuana use and memory appeared in a 2002 issue of The Journal of the American Medical As­sociation and helped to set in motion a series of subsequent stud­ies. Nine Australian researchers compared the attention, memory, problem-solving, and verbal-reasoning skills among four groups of individuals: 102 near-daily marijuana users, 51 long-term marijua­na users, 51 short-term users, and 33 nonusers who made up the control group. The conclusion: “Long-term heavy cannabis users show impairments in memory and attention that endure beyond the period of intoxication and worsen with increasing years of regu­lar cannabis use.”

But the granddaddy of marijuana and learning studies came out in 2012. and astounded even the most cautious researchers. Scien­tists, controlling for factors like years of education, schizophrenia, and the use of alcohol or other drugs, followed a cohort of over one thousand people for more than twenty-five years to investigate the effect of cannabis use on IQ. The study found that using marijua­na regularly before age eighteen resulted in an average IQ of six to eight fewer points at age thirty-eight relative to those who did not use marijuana before age eighteen. This astounding finding was still true for those teens who used marijuana regularly but stopped us­ing the drug after the age of eighteen. “Our hypothesis is that we see this IQ decline in adolescence because the adolescent brain is still developing, and if you introduce cannabis, it might interrupt these critical developmental processes,” said lead author Madeline Meier, a postdoctoral researcher at Duke University.

“I think this is the cleanest study I’ve ever read” exploring the long-term effects of marijuana use, Dr. Nora Volkow, director of the National Institute on Drug Abuse (NIDA), an arm of the National Institutes of Health, told the Associated Press.

The study was criticized in a paper by economist Dr. Ole Rogeberg of the Ragnar Frisch Centre for Economic Research. Dr. Rogeberg criti­cized Meier and her team for failing to control for socio-economic status (SES). The paper received wide media coverage. Policy ana­lyst Wayne Hall said that the “Rogeberg study has been presented as though it was a fairly definitive refutation of the Dunedin study [but] his hypothesis has not been confirmed and that’s been lost in the media coverage.”

When Meier and her colleagues had a chance to reexamine their results, their original conclusion was unchanged. They noted that:

“Dr. Rogeberg’s ideas are interesting, but his challenge is based on simulations. We used actual data on 1,037 people to carry out the analyses he suggested. His ideas are not supported by our data….By restricting our analysis to only include children from middle-class homes, our findings of IQ decline in adolescent-onset cannabis users remain unaltered, thereby suggesting that the decline in IQ cannot be attributed to socioeconomic factors alone….Moreover, we note that our results suggesting that adolescent-onset but not adult-on­set cannabis users showing IQ decline is consistent with findings in rats, and rats have no schooling or SES.”


About fifteen years ago, the floodgates started to open on medi­cal research establishing a connection between marijuana use and mental illness. A lot of this research comes from countries outside the United States, such as Sweden, Britain, and New Zealand.

The first strong suggestion that marijuana use can trigger men­tal problems came in a 1987 study from Sweden published in the British medical journal. Lancet. Researchers did a fifteen-year ex­amination of 45,570 military conscripts and found that those who had used marijuana on more than fifty occasions had a much higher risk—six times higher—of developing schizophrenia relative to nonusers. “Persistence of the association after allowance for other psychiatric illness and social background indicated that cannabis is an independent risk factor for schizophrenia,” concluded the four medical researchers.

Subsequently, evidence from a wide array of studies began to pile up, showing that the more chronic the marijuana use and the earlier in life that marijuana use begins, the greater one’s chances are of developing psychosis typified by delusional thinking and of experiencing the onset of schizophrenia, characterized by a break­down in thought processes.

To assess the overall findings of these mental health studies from around the world, several systematic reviews of this literature have been performed to weigh the sum total of evidence. For ex­ample, a 2007 review in Lancet compared results from thirty-five studies evaluating the impact of marijuana use on the later develop­ment of psychosis, which was defined as delusions, hallucinations, or thought disorders. They concluded that marijuana use signifi­cantly increased the likelihood of developing psychotic symptoms. There was also a dose-response effect, meaning that the more fre­quently marijuana was consumed, the more dramatically the risk of developing psychotic symptoms escalated (up to 200 percent for the most frequent users relative to nonusers). The survey authors concluded: “The evidence is consistent with the view that cannabis increases [the] risk of psychotic outcomes.”

An even larger systematic review of studies—called a meta-analysis—was conducted by Australian researchers in 2011, for the Archives of General Psychiatry, using eighty-three studies to assess the impact of marijuana use on the early onset of psychotic illness. The findings were clear and consistent: “The results of meta-anal­ysis provide evidence for a relationship between cannabis use and earlier onset of psychotic illness…. [The] results suggest the need for renewed warnings about the potentially harmful effects of can­nabis.”

Another link between marijuana and psychotic symptoms sur­faced in research published by a team of eight psychiatrists and researchers in Psychological Medicine in 2010. They discovered that “childhood trauma is associated with both substance [cannabis] misuse and risk for psychosis.” These early childhood traumatizing events can range from physical abuse and sexual molestation, to ne­glect and abandonment. Psychiatric interviews were initiated with 211 adolescents between the ages of twelve and fifteen to identify both their levels of pot use and any early traumatic events in their lives. The researchers concluded that “the presence of both child­hood trauma and early cannabis use significantly increased the risk for psychotic symptoms beyond the risk posed by either risk factor alone, indicating that there was a greater than additive interaction between childhood trauma and cannabis use.”

Still another factor potentially impacting the marijuana and psychosis link is genetic. Several Canadian physicians writing in a 2012 article for Psychiatric Times analyzed the role of certain genes, such as the COMT (Catechol-O-methyltransferase) gene, which have been the subject of numerous studies of psychosis. This particular gene is involved with the metabolism of dopamine in the brain. A variant of this gene slows the breakdown of dopamine which may increase the risk of developing psychosis. Add to this gene variant the use of marijuana, and an even greater risk of psychotic symp­toms is observed.

Even if adolescents or teenagers using marijuana don’t become dependent—and the majority don’t—their brains are still modified by the use of marijuana. It’s this modification of brain structure and function that is at the root of mental health problems later in life. As the California Society of Addiction Medicine aptly puts it on their website: “The overwhelming preponderance of scientific evidence provides adequate rationale for public policies that deter, delay and detect child and adolescent marijuana use.”

Kevin A. Sabet, Reefer Sanity: Seven Great Myths About Marijuana (New York, NY: Beaufort Books, 2013), 34-36, 39-46.

Here is an older update to the post dated 11-11-2014 ~ via The Blaze ~ (I know, ironic):

The study compared 48 people who used marijuana an average of three times a day and 62 non-users. The researchers found a lower IQ in those who smoked the drug as well as a smaller orbitofrontal cortex, a part of the brain associated with addiction and decision making.

They did see more brain connectivity in those who smoked weed, but it wasn’t necessarily a positive thing.

“The results suggest increases in connectivity, both structural and functional that may be compensating for gray matter losses. Eventually, however, the structural connectivity or ‘wiring’ of the brain starts degrading with prolonged marijuana use,” Dr. Sina Aslan, founder and president of the company Advance MRI and a professor at the university, said.

This increased connectivity for a short period of time might be why smokers “seem to be doing fine,” while another part of their brain was reduced, Filbey said.

Filbey acknowledged that this study doesn’t “conclusively address whether any or all of the brain changes are a direct consequence of marijuana use,” but she said “these effects do suggest that these changes are related to age of onset and duration of use.”

Watch this report about the study:

“Medical” Abuse:

Since 1996, 20 states and the District of Columbia have approved “medical marijuana” laws, whereby people who obtain a prescription from a doctor can legally use or purchase marijuana. As in Colorado, many of these supposed medical regimes are degenerating into legalization by another name. Oregon, for example: At the end of 2012, it was home to 56,531 medical-marijuana patients. The majority of these 56,000-plus permissions were approved by only nine doctors. One doctor—an 80-year-old retired heart surgeon in Yakima—approved 4,180 medical-marijuana applications in a span of 12 months. Only 4 percent of Oregon’s medical-marijuana patients, as of the end of 2012, suffered from cancer. Only 1 percent were diagnosed with HIV/AIDS. The large majority, 57 percent, cited unspecified “pain” as the ailment for which treatment was sought. Yet none of the nine doctors who wrote the majority of the marijuana prescriptions was a pain specialist.

Fewer than 2 percent of California card holders have HIV, glaucoma, multiple sclerosis, or cancer: One survey found that the typical California medical-marijuana patient was a healthy 32-year-old man with a history of drug and alcohol abuse. Here, too, some doctors are signing thousands of recommendations after only the scantiest examination—or none at all. An NBC news investigator in Los Angeles visited one dispensary, was examined by a man who later proved to be an acupuncturist and massage therapist, and then received a prescription signed by a doctor who lived 67 miles away….

(Commentary Magazine)

UPDATE via The Daily Mail:

20-Year Study

The terrible truth about cannabis: British expert’s devastating 20-year study finally demolishes claims that smoking pot is harmless

  • One in six teenagers who regularly smoke the drug become dependent
  • It doubles risk of developing psychotic disorders, including schizophrenia
  • Heavy use in adolescence appears to impair intellectual development
  • Driving after smoking cannabis doubles risk of having a car crash
  • Study’s author said: ‘If cannabis is not addictive then neither is heroin’
  • Cannabis users do worse at school. Heavy use in adolescence appears to impair intellectual development
  • One in ten adults who regularly smoke the drug become dependent on it and those who use it are more likely to go on to use harder drugs
  • Smoking it while pregnant reduces the baby’s birth weight.

A definitive 20-year study into the effects of long-term cannabis use has demolished the argument that the drug is safe.

Cannabis is highly addictive, causes mental health problems and opens the door to hard drugs, the study found.

Last night Professor Hall, a professor of addiction policy at King’s College London, dismissed the views of those who say that cannabis is harmless.

‘If cannabis is not addictive then neither is heroin or alcohol,’ he said.

‘It is often harder to get people who are dependent on cannabis through withdrawal than for heroin – we just don’t know how to do it.’ 

Those who try to stop taking cannabis often suffer anxiety, insomnia, appetite disturbance and depression, he found. Even after treatment, less than half can stay off the drug for six months.

The paper states that teenagers and young adults are now as likely to take cannabis as they are to smoke cigarettes.

Professor Hall writes that it is impossible to take a fatal overdose of cannabis, making it less dangerous at first glance than heroin or cocaine. He also states that taking the drug while pregnant can reduce the weight of a baby, and long-term use raises the risk of cancer, bronchitis and heart attack.

But his main finding is that regular use, especially among teenagers, leads to long-term mental health problems and addiction.

‘The important point I am trying to make is that people can get into difficulties with cannabis use, particularly if they get into daily use over a longer period,’ he said. ‘There is no doubt that heavy users experience a withdrawal syndrome as with alcohol and heroin.

‘Rates of recovery from cannabis dependence among those seeking treatment are similar to those for alcohol.’

Mark Winstanley, of the charity Rethink Mental Illness, said: ‘Too often cannabis is wrongly seen as a safe drug, but as this review shows, there is a clear link with psychosis and schizophrenia, especially for teenagers.

‘The common view that smoking cannabis is nothing to get worked up about needs to be challenged more effectively. Instead of classifying and re-classifying, government time and money would be much better spent on educating young people about how smoking cannabis is essentially playing a very real game of Russian roulette with your mental health.’

 …read more…

For a 150+ studies showing brain damage and other serious health links caused by marijuana use, see Popular Technology Net

Let me add something here. I am for the legalization of personal use Marijuana when the authorities can tell if someone is under the influence of it while driving (like they can with drinking and driving… similar to a breathalyzer).

For those interested, I have read books that are pro-Marijuana such as

  • The Emperor Wears No Clothes: The Authoritative Historical Record of Cannabis and the Conspiracy Against Marijuana;
  • Marijuana Myths Marijuana Facts: A Review Of The Scientific Evidence;
  • The Great Book of Hemp: The Complete Guide to the Environmental, Commercial, and Medicinal Uses of the World’s Most Extraordinary Plant.

Granted, these books may be a bit dated, but I guarantee you I have read more on the topic than any pastor I know.

Which leads me to mention, I doubt any person reading this post [that are fighting/arguing for its legalization] have read books like:

1) No Need for Weed: Understanding and Breaking Cannabis Dependency;
2) The Secret Addiction: Overcoming Your Marijuana Dependency;
3) Marijuana: The Unbiased Truth about the World’s Most Popular Weed;
4) Reefer Sanity: Seven Great Myths About Marijuana;
or, 5) The Truth About Pot: Ten Recovering Marijuana Users Share Their Personal Stories.

Below, is Michael Medved responding to a caller and has a fair and balanced response that shows how conservatives should deal with this legislatively.

So what are some positions to discourage use of marijuana by individuals? A few reasons for discouraging use are found at an old post, which some of the above is taken from, but I really suggest just going to PTN. There are immediate implications to a broad legalizing of pot, one is fatalities. One study done by the University of Colorado School of Medicineshows the proportion of marijuana-positive drivers involved in fatal vehicle accidents in Colorado has increased dramatically since the commercialization of medical marijuana in the middle of 2009,” they continue:

Using data from the National Highway Traffic Safety Administration’s Fatality Analysis Reporting System from 1994 to 2011, researchers looked at fatal car accidents in Colorado and the 34 states that didn’t have medical marijuana laws.

They found fatal car crashes in Colorado with at least one driver who tested positive for marijuana was 4.5 percent in the first six months of 1994. In the last six months of 2011, that percentage had jumped to 10 percent. The researchers found no major changes over the same time in the proportion of drivers in fatal crashes in which drivers were alcohol-impaired….

No state should legalize the substance until there are ways — similar to drinking [breathalyzer] — to detect if a person a stoned. Another story shows the insanity in this broad legalizing of a drug that has not only the potential of harming the person using it, but my family when they are on the road ~ NBC reports:

Cordova, who lost a 23-year-old niece and her 1-month-old son to a driver who admitted he smoked pot that day, never smiles back. She thinks legal marijuana in Colorado, where she works, is making the problem of drugged driving worse — and now new research supports her claim.

“Nobody hides it anymore when driving,” Cordova said. “They think it’s a joke because it’s legal. Nobody will take this seriously until somebody loses another loved one.”

As medical marijuana sales expanded into 20 states, legal weed was detected in the bodies of dead drivers three times more often during 2010 when compared to those who died behind the wheel in 1999, according to a new study from Columbia University published in the American Journal of Epidemiology.

“The trend suggests that marijuana is playing an increased role in fatal crashes,” said Dr. Guohua Li, a co-author and director of the Center for Injury Epidemiology and Prevention at Columbia University Medical Center. The researchers examined data from the federal Fatality Analysis Reporting System (FARS), spanning more than 23,000 drivers killed during that 11-year period.


“The increased availability of marijuana and increased acceptance of marijuana use” are fueling the higher rate of cannabinol found in dead drivers, Li told NBC News.

Researchers limited their analysis to California and five others states where toxicology screenings are routinely conducted within an hour of a traffic death. They note that California allowed medical marijuana in 2004. Since then, California has posted “marked increases in driver fatalities testing positive for marijuana,” Li said.

“The number of deaths will grow,” Cordova said. “I’m scared.”

Minutes after the crash that killed Cordova’s niece, Tanya Guevara, and Guevara’s 5-week-old son, police arrested the driver who struck Guevara’s car. Steven Ryan, then 22, admitted to smoking pot earlier that day, according to court records. Ryan later pleaded guilty to vehicular homicide and was sentenced to 10 years in prison in 2012….

Serious stuff, except if your stoned.

So what are some positions to discourage use of marijuana by individuals? Here are just a few reasons and links to a quick synopsis or studies regarding the topic.


Marijuana Withdrawal in Humans: Effects of Oral THC or Divalproex (summary)

Abstinence following daily marijuana use can produce a withdrawal syndrome characterized by negative mood (eg irritability, anxiety, misery), muscle pain, chills, and decreased food intake. Two placebo-controlled, within-subject studies investigated the effects of a cannabinoid agonist, delta-9-tetrahydrocannabinol (THC: Study 1), and a mood stabilizer, divalproex (Study 2), on symptoms of marijuana withdrawal. Participants (n¼7/study), who were not seeking treatment for their marijuana use, reported smoking 6–10 marijuana cigarettes/day, 6–7 days/week. Study 1 was a 15-day in-patient, 5-day outpatient, 15-day in-patient design. During the in-patient phases, participants took oral THC capsules (0, 10 mg) five times/day, 1 h prior to smoking marijuana (0.00, 3.04% THC). Active and placebo marijuana were smoked on in-patient days 1–8, while only placebo marijuana was smoked on days 9–14, that is, marijuana 4 abstinence. Placebo THC was administered each day, except during one of the abstinence phases (days 9–14), when active THC was given. Mood, psychomotor task performance, food intake, and sleep were measured. Oral THC administered during marijuana abstinence decreased ratings of ‘anxious’, ‘miserable’, ‘trouble sleeping’, ‘chills’, and marijuana craving, and reversed large decreases in food intake as compared to placebo, while producing no intoxication. Study 2 was a 58-day, outpatient/in-patient design. Participants were maintained on each divalproex dose (0, 1500 mg/day) for 29 days each. Each maintenance condition began with a 14-day outpatient phase for medication induction or clearance and continued with a 15-day in-patient phase. Divalproex decreased marijuana craving during abstinence, yet increased ratings of ‘anxious’, ‘irritable’, ‘bad effect’, and ‘tired.’ Divalproex worsened performance on psychomotor tasks, and increased food intake regardless of marijuana condition. Thus, oral THC decreased marijuana craving and withdrawal symptoms at a dose that was subjectively indistinguishable from placebo. Divalproex worsened mood and cognitive performance during marijuana abstinence. These data suggest that oral THC, but not divalproex, may be useful in the treatment of marijuana dependence.

Neuropsychopharmacology (2004) 29, 158–170, advance online publication, 15 October 2003; doi:10.1038/sj.npp.1300310


Current and former marijuana use: preliminary findings of a longitudinal study of effects on IQ in young adults

Results: Current marijuana use was significantly correlated (p < 0.05) in a dose- related fashion with a decline in IQ over the ages studied. The comparison of the IQ difference scores showed an average decrease of 4.1 points in current heavy users (p < 0.05) compared to gains in IQ points for light current users (5.8), former users (3.5) and non-users (2.6).

Interpretation: Current marijuana use had a negative effect on global IQ score only in subjects who smoked 5 or more joints per week. A negative effect was not observed among subjects who had previously been heavy users but were no longer using the substance. We conclude that marijuana does not have a long-term negative impact on global intelligence. Whether the absence of a residual marijuana effect would also be evident in more specific cognitive domains such as memory and attention remains to be ascertained.

Health and Perception

The Health Effects of Marijuana: Negative Health Effects Are Numerous

The short-term effects of marijuana include:

Effects on the Brain

The active ingredient in marijuana, delta-9 tetrahydrocannabinol or THC, acts on cannabinoid receptors on nerve cells and influences the activity of those cells. Some brain areas have many cannabinoid receptors, but other areas of the brain have few or none at all. Many cannabinoid receptors are found in the parts of the brain that influence pleasure, memory, thought, concentration, sensory and time perception, and coordinated movement.

When high doses of marijuana are used, usually when eaten in food rather than smoked, users can experience the following symptoms:

Effects on the Heart

Within a few minutes after smoking marijuana, the heart begins beating more rapidly and the blood pressure drops. Marijuana can cause the heart beat to increase by 20 to 50 beats per minute, and can increase even more if other drugs are used at the same time.

Because of the lower blood pressure and higher heart rate, researchers found that users’ risk for a heart attack is four times higher within the first hour after smoking marijuana, compared to their general risk of heart attack when not smoking.

Effects on the Lungs

Smoking marijuana, even infrequently, can cause burning and stinging of the mouth and throat, and cause heavy coughing. Scientists have found that regular marijuana smokers can experience the same respiratory problems as tobacco smokers do, including:

Most marijuana smokers consume a lot less cannabis than cigarette smokers consume tobacco, however the harmful effects of smoking marijuana should not be ignored. Marijuana contains more carcinogenic hydrocarbons than tobacco smoke and because marijuana smokers typically inhale deeper and hold the smoke in their lungs longer than tobacco smokers, their lungs are exposed to those carcinogenic properties longer, when smoking.

What About Cancer?

Although one study found that marijuana smokers were three times more likely to develop cancer of the head or neck than non-smokers, that study could not be confirmed by further analysis.

Because marijuana smoke contains three times the amount of tar found in tobacco smoke and 50 percent more carcinogens, it would seem logical to deduce that there is an increased risk of lung cancer for marijuana smokers. However, researchers have not been able to definitively prove such a link because their studies have not been able to adjust for tobacco smoking and other factors that might also increase the risk.

Studies linking marijuana smoking to lung cancer have also been limited by selection bias and small sample size. For example, the participants in those studies may have been too young to have developed lung cancer yet. Even though researchers have yet to “prove” a link between smoking pot and lung cancer, regular smokers may want to consider the risk.

 Other Health Effects

Research indicates that THC impairs the body’s immune system from fighting disease, which can cause a wide variety of health problems. One study found that marijuana actually inhibited the disease-preventing actions of key immune cells. Another study found that THC increased the risk of developing bacterial infections and tumors.


See Also: NIDA InfoFacts: Marijuana

Immune System


The most potent argument against the use of marijuana to treat medical disorders is that marijuana may cause the acceleration or aggravation of the very disorders it is being used to treat.

Smoking marijuana regularly (a joint a day) can damage the cells in the bronchial passages which protect the body against inhaled microorganisms and decrease the ability of the immune cells in the lungs to fight off fungi, bacteria, and tumor cells. For patients with already weakened immune systems, this means an increase in the possibility of dangerous pulmonary infections, including pneumonia, which often proves fatal in AIDS patients.

Studies further suggest that marijuana is a general “immunosuppressant” whose degenerative influence extends beyond the respiratory system. Regular smoking has been shown to materially affect the overall ability of the smoker’s body to defend itself against infection by weakening various natural immune mechanisms, including macrophages (a.k.a. “killer cells”) and the all-important T-cells. Obviously, this suggests the conclusion, which is well-supported by scientific studies, that the use of marijuana as a medical therapy can and does have a very serious negative effect on patients with pre-existing immune deficits resulting from AIDS, organ transplantation, or cancer chemotherapy, the very conditions for which marijuana has most often been touted and suggested as a treatment. It has also been shown that marijuana use can accelerate the progression of HIV to full-blown AIDS and increase the occurrence of infections and Kaposi’s sarcoma. In addition, patients with weak immune systems will be even less able to defend themselves against the various respiratory cancers and conditions to which consistent marijuana use has been linked, and which are discussed briefly under “Respiratory Illnesses.”

In conclusion, it seems that the potential dangers presented by the medical use of marijuana may actually contribute to the dangers of the diseases which it would be used to combat. Therefore, I suggest that marijuana should not be permitted as a therapy, at least until a good deal more conclusive research has been completed concerning its debilitating effect on the immune system.

For more on this topic, please see Donald P. Tashkin, M.D., “Effects of Marijuana on the Lung and Its Immune Defenses,” Secretary’s Youth Substance Abuse Prevention Intiative: Resource Papers, March 1997, Center for Substance Abuse Prevention. Pages 33-51 of this address can be found at the website of the Indiana Prevention Resource Center at Indiana University, located at marijuana.html.

Early Onset of Schizophrenia

Marijuana / Cannabis and Schizophrenia

Overview: Use of street drugs (including LSD,methamphetamine,marijuana/hash/cannabis) and alcohol have been linked with significantly increased probability of developing psychosis and schizophrenia. This link has been documented in over 30 different scientific studies (studies done mostly in the UK, Australia and Sweden) over the past 20 years. In one example, a study interviewed 50,000 members of the Swedish Army about their drug consumption and followed up with them later in life. Those who were heavy consumers of cannabis at age 18 were over 600% more likely to be diagnosed with schizophrenia over the next 15 years than those did not take it. (see diagram below). Experts estimate that between 8% and 13% of all schizophrenia cases are linked to marijuna / cannabis use during teen years.

Many of these research studies indicate that the risk is higher when the drugs are used by people under the age of 21, a time when the human brain is developing rapidly and is particularly vulnerable.

People with any biological predisposition towards schizophrenia are at the highest risk — unfortunately its impossible to accurately identify this predisposition beforehand ( a family history of mental illness is just one indicator of such a predisposition). [see causes and prevention of schizophrenia for more information on all risk factors linked to a person developing schizophrenia]

Researchers in New Zealand found that those who used cannabis by the age of 15 were more than three times (300%) more likely to develop illnesses such as schizophrenia. Other research has backed this up, showing that cannabis use increases the risk of psychosis by up to 700% for heavy users, and that the risk increases in proportion to the amount of cannabis used (smoked or consumed). Additionally, the younger a person smokes/uses cannabis, the higher the risk for schizophrenia, and the worse the schizophrenia is when the person does develop it. Research by psychiatrists in inner-city areas speak of cannabis being a factor in up to 80 percent of schizophrenia cases.

Professor Robin Murray (London Institute of Psychiatry) has recently (2005) completed a 15-year study of more than 750 adolescents in conjunction with colleagues at King’s College London and the University of Otago in New Zealand.

Overall people were 4.5 times more likely to be schizophrenic at 26 if they were regular cannabis smokers at 15, compared to 1.65 times for those who did not report regular use until age 18.

Impaired Driving

Facts for Teens

Smoking Marijuana Can Make Driving Dangerous

The cerebellum is the section of our brain that controls balance and coordination. When THC affects the cerebellum’s function, it makes scoring a goal in soccer or hitting a home run pretty tough. THC also affects the basal ganglia, another part of the brain that’s involved in movement control.

These THC effects can cause disaster on the road. Research shows that drivers on marijuana have slower reaction times, impaired judgment, and problems responding to signals and sounds. Studies conducted in a number of localities have found that approximately 4 to 14 percent of drivers who sustained injury or death in traffic accidents tested positive for THC.

The National Institutes of Health issues the impairment experienced by drivers who are high: “Marijuana significantly impairs judgment, motor coordination, and reaction time, and studies have found a direct relationship between blood THC concentration and impaired driving ability.” (See references at the link.) Time Magazine had an interesting study it wrote about

To find out, the study recruited 18 occasional cannabis smokers, 13 of them men, between the ages 21 and 37. The participants took six 45-minute drives in a driving simulator—a 1996 Malibu sedan mounted in a 7.3 diameter dome—at the University of Iowa. Each drive tested a different combination of high or low concentration THC, alcohol, and placebos (to create a placebo, participants were given fruit juice with alcohol swabbed in the rim, topped of with 1ml alcohol, to mimic alcohol’s smell and taste).

The researchers looked at 250 parameters of driving ability, but this paper focused on three in particular: weaving within the lane, the number of times the car left the lane, and the speed of the weaving. While alcohol had an effect on the number of times the car left the lane and the speed of the weaving, marijuana did not. Marijuana did show an increase in weaving. Drivers with blood concentrations of 13.1 ug/L THC, the psychoactive ingredient in cannabis, showed increase weaving that was similar to those with a .08 breath alcohol concentration, the legal limit in most states. For reference, 13.1 ug/L THC is more than twice the 5 ug/L numeric limit in Washington and Colorado.

Dr. Marilyn Huestis, the principal investigator in the study, says it is important to note that the study looked at the concentration of THC in the driver’s system while they were driving. This is quite different from the concentration typically measured in a drugged driver out on the road, whose blood may not be checked until several hours after an arrest, allowing the THC level to drop considerably from the time they were driving….


The study also found that pot and alcohol have more of an impact on driving when used together. Drivers who used both weaved within lanes, even if their blood THC and alcohol concentrations were below the threshold for impairment taken on their own. “We know cannabis is primarily found with a low dose of alcohol,” Huestis says. “Many young people have a couple beers and then cannabis.”


The number of drivers involved in fatal crashes who tested positive for activeTHC, the main psychoactive compound in marijuana, had held fairly steady from 2010 to 2013 — between 32 and 38 per year. That number jumped to 75 in 2014, and about half were above the state’s legal limit for marijuana-impaired driving, Baldwin said.

Many of those drivers also tested positive for alcohol or other drugs…

(The Oragonian)

YES, but the point is that legalization increases use, which we know when combined with alcohol, increases the affects of THC: “The study also found that pot and alcohol have more of an impact on driving when used together” (Time).