Myth: Marijuana's Harms Have Been Proved Scientifically. In the 1960s and 1970s, many people believed that marijuana was harmless. Today we know that marijuana is much more dangerous than previously believed.
Fact: In 1972, after reviewing the scientific evidence, the National Commission on Marihuana and Drug Abuse concluded that while marijuana was not entirely safe, its dangers had been grossly overstated. Since then, researchers have conducted thousands of studies of humans, animals, and cell cultures. None reveal any findings dramatically different from those described by the National Commission in 1972. In 1995, based on thirty years of scientific research editors of the British medical journal Lancet concluded that "the smoking of cannabis, even long term, is not harmful to health."
Myth: Marijuana Has No Medicinal Value. Safer, more effective drugs are available. They include a synthetic version of THC, marijuana's primary active ingredient, which is marketed in the United States under the name Marinol.
Fact: Marijuana has been shown to be effective in reducing the nausea induced by cancer chemotherapy, stimulating appetite in AIDS patients, and reducing intraocular pressure in people with glaucoma. There is also appreciable evidence that marijuana reduces muscle spasticity in patients with neurological disorders. A synthetic capsule is available by prescription, but it is not as effective as smoked marijuana for many patients. Pure THC may also produce more unpleasant psychoactive side effects than smoked marijuana. Many people use marijuana as a medicine today, despite its illegality. In doing so, they risk arrest and imprisonment.
Myth: Marijuana is Highly Addictive. Long term marijuana users experience physical dependence and withdrawal, and often need professional drug treatment to break their marijuana habits.
Fact: Most people who smoke marijuana smoke it only occasionally. A small minority of Americans - less than 1 percent - smoke marijuana on a daily basis. An even smaller minority develop a dependence on marijuana. Some people who smoke marijuana heavily and frequently stop without difficulty. Others seek help from drug treatment professionals. Marijuana does not cause physical dependence. If people experience withdrawal symptoms at all, they are remarkably mild.
Myth: Marijuana is a Gateway Drug. Even if marijuana itself causes minimal harm, it is a dangerous substance because it leads to the use of "harder drugs" like heroin, LSD, and cocaine.
Fact: Marijuana does not cause people to use hard drugs. What the gateway theory presents as a causal explanation is a statistic association between common and uncommon drugs, an association that changes over time as different drugs increase and decrease in prevalence. Marijuana is the most popular illegal drug in the United States today. Therefore, people who have used less popular drugs such as heroin, cocaine, and LSD, are likely to have also used marijuana. Most marijuana users never use any other illegal drug. Indeed, for the large majority of people, marijuana is a terminus rather than a gateway drug.
Myth: Marijuana Offenses Are Not Severely Punished. Few marijuana law violators are arrested and hardly anyone goes to prison. This lenient treatment is responsible for marijuana continued availability and use.
Fact: Marijuana arrests in the United States doubled between 1991 and 1995. In 1995, more than one-half-million people were arrested for marijuana offenses. Eighty-six percent of them were arrested for marijuana possession. Tens of thousands of people are now in prison or marijuana offenses. An even greater number are punished with probation, fines, and civil sanctions, including having their property seized, their driver's license revoked, and their employment terminated. Despite these civil and criminal sanctions, marijuana continues to be readily available and widely used.
Myth: Marijuana Policy in the Netherlands is a Failure. Dutch law, which allows marijuana to be bought, sold, and used openly, has resulted in increasing rates of marijuana use, particularly in youth.
Fact: The Netherlands' drug policy is the most nonpunitive in Europe. For more than twenty years, Dutch citizens over age eighteen have been permitted to buy and use cannabis (marijuana and hashish) in government-regulated coffee shops. This policy has not resulted in dramatically escalating cannabis use. For most age groups, rates of marijuana use in the Netherlands are similar to those in the United States. However, for young adolescents, rates of marijuana use are lower in the Netherlands than in the United States. The Dutch people overwhelmingly approve of current cannabis policy which seeks to normalize rather than dramatize cannabis use. The Dutch government occasionally revises existing policy, but it remains committed to decriminalization.
Myth: Marijuana Kills Brain Cells. Used over time, marijuana permanently alters brain structure and function, causing memory loss, cognitive impairment, personality deterioration, and reduced productivity.
Fact: None of the medical tests currently used to detect brain damage in humans have found harm from marijuana, even from long term high-dose use. An early study reported brain damage in rhesus monkeys after six months exposure to high concentrations of marijuana smoke. In a recent, more carefully conducted study, researchers found no evidence of brain abnormality in monkeys that were forced to inhale the equivalent of four to five marijuana cigarettes every day for a year. The claim that marijuana kills brain cells is based on a speculative report dating back a quarter of a century that has never been supported by any scientific study.
Myth: Marijuana Causes an Amotivational Syndrome. Marijuana makes users passive, apathetic, and uninterested in the future. Students who use marijuana become underachievers and workers who use marijuana become unproductive.
Fact: For twenty-five years, researchers have searched for a marijuana-induced amotivational syndrome and have failed to find it. People who are intoxicated constantly, regardless of the drug, are unlikely to be productive members of society. There is nothing about marijuana specifically that causes people to lose their drive and ambition. In laboratory studies, subjects given high doses of marijuana for several days or even several weeks exhibit no decrease in work motivation or productivity. Among working adults, marijuana users tend to earn higher wages than non-users. College students who use marijuana have the same grades as nonusers. Among high school students, heavy use is associated with school failure, but school failure usually comes first.
Myth: Marijuana Impairs Memory and Cognition. Under the influence of marijuana, people are unable to think rationally and intelligently. Chronic marijuana use causes permanent mental impairment.
Fact: Marijuana produces immediate, temporary changes in thoughts, perceptions, and information processing. The cognitive process most clearly affected by marijuana is short-term memory. In laboratory studies, subjects under the influence of marijuana have no trouble remembering things they learned previously. However, they display diminished capacity to learn and recall new information. This diminishment only lasts for the duration of the intoxication. There is no convincing evidence that heavy long-term marijuana use permanently impairs memory or other cognitive functions.
Myth: Marijuana Can Cause Permanent Mental Illness. Among adolescents, even occasional marijuana use may cause psychological damage. During intoxication, marijuana users become irrational and often behave erratically.
Fact: There is no convincing scientific evidence that marijuana causes psychological damage or mental illness in either teenagers or adults. Some marijuana users experience psychological distress following marijuana ingestion, which may include feelings of panic, anxiety, and paranoia. Such experiences can be frightening, but the effects are temporary. With very large doses, marijuana can cause temporary toxic psychosis. This occurs rarely, and almost always when marijuana is eaten rather than smoked. Marijuana does not cause profound changes in people's behavior.
Myth: Marijuana Causes Crime. Marijuana users commit more property offenses than nonusers. Under the influence of marijuana, people become irrational, aggressive, and violent.
Fact: Every serious scholar and government commission examining the relationship between marijuana use and crime has reached the same conclusion: marijuana does not cause crime. The vast majority of marijuana users do not commit crimes other than the crime of possessing marijuana. Among marijuana users who do commit crimes, marijuana plays no causal role. Almost all human and animal studies show that marijuana decreases rather than increases aggression.
Myth: Marijuana Interferes With Male and Female Sex Hormones. In both men and women, marijuana can cause infertility. Marijuana retards sexual development in adolescents. It produces feminine characteristics in males and masculine characteristics in females.
Fact: There is no evidence that marijuana causes infertility in men or women. In animal studies, high doses of THC diminish the production of some sex hormones and can impair reproduction. However, most studies of humans have found that marijuana has no impact of sex hormones. In those studies showing an impact, it is modest, temporary, and of no apparent consequence for reproduction. There is no scientific evidence that marijuana delays adolescent sexual development, has feminizing effect on males, or a masculinizing effect on females.
Myth: Marijuana Use During Pregnancy Damages the Fetus. Prenatal marijuana exposure causes birth defects in babies, and, as they grow older, developmental problems. The health and well being of the next generation is threatened by marijuana use by pregnant women.
Fact: Studies of newborns, infants, and children show no consistent physical, developmental, or cognitive deficits related to prenatal marijuana exposure. Marijuana had no reliable impact on birth size, length of gestation, neurological development, or the occurrence of physical abnormalities. The administration of hundreds of tests to older children has revealed only minor differences between offspring of marijuana users and nonusers, and some are positive rather than negative. Two unconfirmed case-control studies identified prenatal marijuana exposure as one of many factors statistically associated with childhood cancer. Given other available evidence, it is highly unlikely that marijuana causes cancer in children.
Myth: Marijuana Use Impairs the Immune System. Marijuana users are at increased risk of infection, including HIV. AIDS patients are particularly vulnerable to marijuana's immunopathic effects because their immune systems are already suppressed.
Fact: There is no evidence that marijuana users are more susceptible to infections than nonusers. Nor is there evidence that marijuana lowers users' resistance to sexually transmitted diseases. Early studies which showed decreased immune function in cells taken from marijuana users have since been disproved. Animals given extremely large doses of THC and exposed to a virus have higher rates of infection. Such studies have little relevance to humans. Even among people with existing immune disorders, such as AIDS, marijuana use appears to be relatively safe. However, the recent finding of an association between tobacco smoking and lung infection in AIDS patients warrants further research into possible harm from marijuana smoking in immune suppressed persons.
Myth: Marijuana is More Damaging to the Lungs Than Tobacco. Marijuana smokers are at a high risk of developing lung cancer, bronchitis, and emphysema.
Fact: Moderate smoking of marijuana appears to pose minimal danger to the lungs. Like tobacco smoke, marijuana smoke contains a number of irritants and carcinogens. But marijuana users typically smoke much less often than tobacco smokers, and over time, inhale much less smoke. As a result, the risk of serious lung damage should be lower in marijuana smokers. There have been no reports of lung cancer related solely to marijuana, and in a large study presented to the American Thoracic Society in 2006, even heavy users of smoked marijuana were found not to have any increased risk of lung cancer. Unlike heavy tobacco smokers, heavy marijuana smokers exhibit no obstruction of the lung's small airway. That indicates that people will not develop emphysema from smoking marijuana.
Myth: Marijuana's Active Ingredient, THC, Gets Trapped in Body Fat. Because THC is released from fat cells slowly, psychoactive effects may last for days or weeks following use. THC's long persistence in the body damages organs that are high in fat content, the brain in particular.
Fact: Many active drugs enter the body's fat cells. What is different (but not unique) about THC is that it exits fat cells slowly. As a result, traces of marijuana can be found in the body for days or weeks following ingestion. However, within a few hours of smoking marijuana, the amount of THC in the brain falls below the concentration required for detectable psychoactivity. The fat cells in which THC lingers are not harmed by the drug's presence, nor is the brain or other organs. The most important consequence of marijuana's slow excretion is that it can be detected in blood, urine, and tissue long after it is used, and long after its psychoactivity has ended.
Myth: Marijuana Use is a Major Cause Of Highway Accidents. Like alcohol, marijuana impairs psychomotor function and decreases driving ability. If marijuana use increases, an increase in of traffic fatalities is inevitable.
Fact: There is no compelling evidence that marijuana contributes substantially to traffic accidents and fatalities. At some doses, marijuana affects perception and psychomotor performances- changes which could impair driving ability. However, in driving studies, marijuana produces little or no car-handling impairment- consistently less than produced by low moderate doses of alcohol and many legal medications. In contrast to alcohol, which tends to increase risky driving practices, marijuana tends to make subjects more cautious. Surveys of fatally injured drivers show that when THC is detected in the blood, alcohol is almost always detected as well. For some individuals, marijuana may play a role in bad driving. The overall rate of highway accidents appears not to be significantly affected by marijuana's widespread use in society.
Myth: Marijuana Related Hospital Emergencies Are Increasing, Particularly Among Youth. This is evidence that marijuana is much more harmful than most people previously believed.
Fact: Marijuana does not cause overdose deaths. The number of people in hospital emergency rooms who say they have used marijuana has increased. On this basis, the visit may be recorded as marijuana-related even if marijuana had nothing to do with the medical condition preceding the hospital visit. Many more teenagers use marijuana than use drugs such as heroin and cocaine. As a result, when teenagers visit hospital emergency rooms, they report marijuana much more frequently than they report heroin and cocaine. In the large majority of cases when marijuana is mentioned, other drugs are mentioned as well. In 1994, fewer than 2% of drug related emergency room visits involved the use of marijuana.
Myth: Marijuana Is More Potent Today Than In The Past. Adults who used marijuana in the 1960s and 1970s fail to realize that when today's youth use marijuana they are using a much more dangerous drug.
Fact: When today's youth use marijuana, they are using the same drug used by youth in the 1960s and 1970s. A small number of low-THC sample sized by the Drug Enforcement Administration are used to calculate a dramatic increase in potency. However, these samples were not representative of the marijuana generally available to users during this era. Potency data from the early 1980s to the present are more reliable, and they show no increase in the average THC content of marijuana. Even if marijuana potency were to increase, it would not necessarily make the drug more dangerous. Marijuana that varies quite substantially in potency produces similar psychoactive effects.
Myth: Marijuana Use Can Be Prevented. Drug education and prevention programs reduced marijuana use during the 1980s. Since then, our commitment has slackened, and marijuana use has been rising. By expanding and intensifying current anti-marijuana messages, we can stop youthful experimentation.
Fact: There is no evidence that anti-drug messages diminish young people's interest in drugs. Anti-drug campaigns in the schools and the media may even make drugs more attractive. Marijuana use among youth declined throughout the 1980s, and began increasing in the 1990s. This increase occurred despite young people's exposure to the most massive anti-marijuana campaign in American history. In a number of other countries, drug education programs are based on a "harm reduction" model, which seeks to reduce the drug-related harm among those young people who do experiment with drugs.
Highlights from the book Marijuana Myths, Marijuana Facts: A Review of the Scientific Evidence. By Drs. Lynn Zimmer and John Morgan. New York: The Lindesmith Center, 1997.