THE LINDESMITH CENTER [#] Exposing Marijuana Myths: A Review of the Scientific Evidence ---------------------------------------------------------------------------- Lynn Zimmer Associate Professor of Sociology, Queens College John P. Morgan Professor of Pharmacology, City University of New York Medical School The Lindesmith Center, 1995 ---------------------------------------------------------------------------- INTRODUCTION Since the 1920s, supporters of marijuana prohibition have exaggerated the drug's dangers. In different eras, different claims have gained prominence, but few have ever been abandoned. Indeed, many of the "reefer madness" tales that were used to generate support for early anti-marijuana laws continue to appear in government and media reports today. For a while in the 1970s, it seemed as if scientific inquiries were beginning to influence the government's marijuana policies. Following thorough reviews of the existing evidence by scholars and official commissions, criminal penalties for marijuana offenses were lessened and a number of states moved in the direction of decriminalization. However, in response to lingering concerns about marijuana's potential toxicity, the government expanded its funding of scientific research, mostly through the newly created National Instutite on Drug Abuse (NIDA). Probably the most important studies of the 1970s were three large "field studies" in Greece, Costa Rica and Jamaica. These studies, which evaluated the impact of marijuana on users in their natural environments, were supplemented by clinical examinations and laboratory experiments oriented toward answering the questions about marijuana that continued to be debated in the scientific literature. The data from these studies, published in numerous books and scholarly journals, covered such matters as marijuana's effects on the brain, lungs, immune and reproductive systems, its impact on personality, development, and motivational states, and its addictive potential. Although these studies did not answer all remaining questions about marijuana toxicity, they generally supported the idea that marijuana was a relatively safe drug -- not totally free from potential harm, but unlikely to create serious harm for most individual users or society. In the years since, thousands of additional studies have been conducted, many of them funded by NIDA, and together they reaffirm marijuana's substantial margin of safety. Our review of that body of work reveals an occasional study indicating greater toxicity than previously thought. But in nearly all such cases, the methodologies were seriously flawed and the findings could not be replicated by other researchers. Especially since the 1980s, when the federal government's renewed war on cannabis began, both the funding of marijuana research and the dissemination of its findings have been highly politicized. Indeed, NIDA's role seems to have become one of service to the War on Drugs. Dozens of claims of toxicity appear in its documents, despite the existence of scores of scientific studies refuting their validity. At the same time, studies that fail to find serious toxicity are ignored. In the following pages, we review the scientific evidence surrounding the most prominent of the anti-marijuana claims. CLAIM #1: MARIJUANA USE IS INCREASING AT AN ALARMING RATE Reports of a recent slight increase in marijuana use, especially among youth, are being used to convince Americans that a renewed campaign about the drug's dangers is necessary to avert an impending epidemic. THE FACTS According to government surveys of the general population, marijuana use began decreasing in 1980, after more than a decade of steady increase. By 1990, the downward trend showed signs of slowing, but use-rates remained substantially lower than those recorded in the 1970s. For example, among 12-17 year olds, past year marijuana use was about 8 percent in 1992, compared to 24.1 percent in 1979. Among 18-25 year olds, past year use was 23 percent in 1992, compared to 46.9 percent in 1979. A separate survey of high school students shows similar trends, with use-rates in the 1990s well below those reported in the 1970s. However, after reaching an all-time low in 1992, they increased slightly during the next two years. Lifetime Prevalence of Marijuana, High Schools Seniors, 1976-1994 1976 1978 1980 1982 19841986 1988 1990 19921994 52.8 59.2 60.3 58.7 54.950.9 47.2 40.7 32.638.2 The High School Survey was originally conceived by the National Institute on Drug Abuse (NIDA) as a measure of non-pathological drug use. This is still what it measures. Adolescence is a time of experimentation, with drug use as well as other activities. Most adolescent drug users do not go on to become "drug abusers." Indeed, most adolescent drug users, after a few years of experimentation, cease using illegal drugs altogether. We will probably never know why marijuana-use rates go up and down over time. However, it is worth noting that the recent increase occurred among the same population of young people who had been exposed to a decade-long anti-marijuana campaign in the schools and the media. That campaign, based on exaggerations of marijuana's harms and a "just say no" ideology, has clearly failed. Young people, and Americans generally, need to know the scientific evidence about marijuana if they are to make informed decisions about both their own drug use and the future of American drug policy. CLAIM #2: MARIJUANA POTENCY HAS INCREASED SUBSTANTIALLY The claim that there has been a 10-, 20- or 30-fold increase in marijuana potency since the 1970s is used to discredit previous studies that showed minimal harm caused by the drug and convince users from earler eras that today's marijuana is much more dangerous. THE FACTS For more than 20 years the government-funded Potency Monitoring Project (PMP) at the University of Mississippi has been analyzing samples of marijuana submited by U.S. law enforcement officials. At no time have police seizures reflected the marijuana generally available to users around the country and, in the 1970s, they were over-represented by large-volume low-potency Mexican kilobricks. During the 1970s, the PMP regularly reported potency averages of under 1%, with a low of 0.4% in 1974. Quite clearly, these averages under-estimate the THC content of marijuana smoked during this period. Marijuana of under 0.5% potency has almost no psychoactivity. While it is possible that people sometimes obtained marijuana of such low potency, for the drug to have become popular in the 1960s and 1970s, most people must have regularly obtained marijuana with higher THC content. Until the late 1970s, PMP samples included none of the traditionally higher-potency cannabis products, such as buds and sinsemilla, even though these products were available on the retail market. When changes in police practices resulted in their seizure, PMP potency averages increased. Every independent analysis of potency in the 1970s found higher THC averages than the PMP. For example, the 59 samples submitted to PharmChem Laboratories in 1973 averaged 1.62%; only 16 (27%) contained less than 1% THC, more than half were over 2% and about one-fifth were over 4%. In 1975, PharmChem samples ranged from 2 to 5%, with some as high as 14% -- nearly 30 times the .71 average reported by the PMP. After 1980, both the number and variety of official seizures increased dramatically, improving the validity of the PMP's reported averages, although they continue to be based on "convenience" rather than "representative" samples. As shown below, average potency has remained essentially unchanged since the early 1980s: Mean Percentage THC of Seized Marijuana, 1981-1993, Mississippi Monitoring Project 1981 1982 1983 1984 19851986 1987 1988 19891990 1991 1992 1993 2.28 3.05 3.23 2.39 2.822.30 2.93 3.29 3.063.36 3.36 3.00 3.32 Even if potency had increased slightly since the 1970s, it would not mean that smoking marijuana had become more dangerous. In fact, since the primary health risk of marijuana comes from smoking, higher potency products can be less dangerous because they allow people to achieve the desired effect by inhaling less. CLAIM #3: MARIJUANA IS A DRUG WITHOUT THERAPEUTIC VALUE Proposals to make marijuana legally available as a medicine are countered with claims that safer, more effective drugs are available, including a synthetic version of delta-9-THC, marijuana's primary active ingredient. THE FACTS For thousands of years, throughout the world, people have used marijuana to treat a variety of medical conditions. Today, in the United States, such use is prohibited. Although thirty-six states have passed legislation to allow marijuana's use as a medicine, federal law preempts their making marijuana legally available to patients. A number of studies have shown that marijuana is effective in reducing nausea and vomiting, lowering intraocular pressure associated with glaucoma, and decreasing muscle spasm and spasticity. Today, many people use marijuana for these and other medical purposes, despite its illegal status. People undergoing cancer chemotherapy have found smoked marijuana to be an effective anti-nauseant-often more effective than available pharmaceutical medications. Indeed, 44 percent of oncologists responding to a questionnaire said they had recommended marijuana to their cancer patients; others said they would recommend it if it were legal. Marijuana is also smoked by thousands of AIDS patients to treat the nausea and vomiting associated with both the disease and AZT drug therapy. Because it stimulates appetite, marijuana also counters HIV-related "wasting," allowing AIDS patients to gain weight and prolong their lives. In 1986, a synthetic delta-9-THC capsule (Marinol) was marketed in the United States and labeled for use as an anti-emetic. Despite some utility, this product has serious drawbacks, including its cost. For example, a patient taking three 5 mgm capsules a day would spend over $5,000 to use Marinol for one year. In comparison to the natural, smokeable product Marinol also has some pharmacological shortcomings. Because THC delivered in oral capsules enters the bloodstream slowly, it yields lower serum concentrations per dose. Oral THC circulates in the body longer at effective concentrations, and more of it is metabolized to an active compound; thus, it more frequently yields unpleasant psychoactive effects. In patients suffering from nausea, the swallowing of capsules may itself provoke vomiting. In short, the smoking of crude marijuana is more efficient in delivering THC and, in some cases, it may be more effective. The continuing illegality of medical marijuana is based more on political than scientific considerations. Although during the 1970s the government supported exploration into marijuana's therapeutic potential, its role has become one of blocking new research and opposing any change in marijuana's legal status. CLAIM #4: MARIJUANA CAUSES LUNG DISEASE It is frequently claimed that marijuana smoke contains such high concentrations of irritants that marijuana users' risk of developing lung disease is equal to or greater than that of tobacco users. THE FACTS Except for their psychoactive ingredients, marijuana and tobacco smoke are nearly identical. Because most marijuana smokers inhale more deeply and hold the smoke in their lungs, more dangerous material may be consumed per cigarette. However, it is the total volume of irritant inhalation-not the amount in each cigarette-that matters. Most tobacco smokers consume more than 10 cigarettes per day and some consume 40 or more. Regular marijuana smokers seldom consume more than 3-5 cigarettes per day and most consume far fewer. Thus, the amount of irritant material inhaled almost never approaches that of tobacco users. Frequent marijuana smokers experience adverse respiratory symptoms from smoking, including chronic cough, chronic phlegm, and wheezing. However, the only prospective clinical study shows no increased risk of crippling pulmonary disease (chronic bronchitis and emphysema). Since 1982, UCLA researchers have evaluated pulmonary function and bronchial cell characteristics in marijuana-only smokers, tobacco-only smokers, smokers of both, and non-smokers. Although they have found changes in marijuana-only smokers, the changes are much less pronounced than those found in tobacco smokers. The nature of the marijuana-induced changes were also different, occuring primarily in the lung's large airways-not the small peripheral airways affected by tobacco smoke. Since it is small-airway inflamation that causes chronic bronchitis and emphysema, marijuana smokers may not develop these diseases. In an epidemiological survey, approximately 1200 subjects gave information on smoking and pulmonary function at 2-year intervals. A large percentage of the subjects underwent pulmonary function testing. Although a small group who reported previous marijuna smoking had significant pulmonary abnormalities, curent marijuana smokers had no significant reduction in any pulmonary functions. There are no epidemiological or aggregate clinical data suggesting that marijuana-only smokers develop lung cancer. However, since some bronchial cell changes appear to be pre-cancerous, an increased risk of cancer among frequent marijuana smokers is possible. Since the pulmonary risks associated with marijuana are related to smoking, the danger is eliminated with other routes of administration. For committed smokers, pulmonary risk might be reduced with higher-potency products, which produce desired psychoactive effects with less inhalation of irritants. Smokers could also be encouraged to abandon deep inhalation and breath-holding, which increase drug delivery only slightly. Finally, pulmonary risk might be reduced if marijuana were smoked in water pipes rather than cigarettes. CLAIM #5: MARIJUANA IMPAIRS IMMUNE SYSTEM FUNCTIONING It has been widely claimed that marijuana substantially increases users' risk of contracting various infectious diseases. First emerging in the 1970s, this claim took on new significance in the 1980s, following reports of marijuana use by people suffering from AIDS. THE FACTS The principal study fueling the original claim of immune impairment involved preparations created with white blood cells that had been removed from marijuana smokers and controls. After exposing the cells to known immune activators, researchers reported a lower rate of "transformation" in those taken from marijuana smokers. However, numerous groups of scientists, using similar techniques, have failed to confirm this original study. In fact, a 1988 study demonstrated an increase in responsiveness when white blood cells from marijuana smokers were exposed to immunological activators. Studies involving laboratory animals have shown immune impairment following administration of THC, but only with the use of extremely high doses. For example, one study demonstrated an increase in herpes infection in rodents given doses of 100 mg/kg/day-a dose approximately 1000 times the dose necessary to produce a psychoactive effect in humans. There have been no clinical or epidemiological studies showing an increase in bacterial, viral, or parasitic infection among human marijuana users. In three large field studies conducted in the 1970s, in Jamaica, Costa Rica and Greece, researchers found no differences in disease susceptibility between marijuana users and matched controls. Marijuana use does not increase the risk of HIV infection; nor does it increase the onset or intensity of symptoms among AIDS patients. In fact, the FDA decision to approve the use of Marinol (synthetic THC) for use in HIV-wasting syndrome relied upon the absence of any immunopathology due to THC. Today, thousands of people with AIDS are smoking marijuana daily to combat nausea and increase appetite. There is no scientific basis for claims that this practice compromises their immune responses. Indeed, the recent discovery of a peripheral cannabinoid receptor asociated with lymphatic tissue should encourage aggressive exploration of THC's potential use as an immune-system stimulant. CLAIM #6: MARIJUANA HARMS SEXUAL MATURATION AND REPRODUCTION Marijuana has been said to interfere with the production of hormones associated with reproduction, causing possible infertility among adult users and delayed sexual development among adolescents. THE FACTS There is no evidence that marijuana impairs male reproductive functioning. The Jamaican and Costa Rican field studies detected no differences in hormone levels between marijuana users and non-users. In epidemiological surveys of marijuana users, no problems with fertility have emerged as important. In 1974, researchers reported diminished testosterone, reduced sexual function and abnormal sperm cells in males identified as chronic marijuana users. In a laboratory study, the same researchers reported an acute decrease in testosterone, but no chronic effect after nine weeks of smoking; they did not evaluate sperm volume or quality. In other laboratory studies, researchers have been generally unable to replicate these findings although by administering very high THC doses-up to 20 cigarettes per day for 30 days- one study found a slight decrease in sperm concentrations. In all studies, test results remained within normal ranges and probably would not have affected actual fertility. Severe adverse consequences have also been produced in male laboratory animals, although only with extremely high daily THC doses. More importantly, in both the human and animal laboratory studies, all observed changes were reversed once THC adminstration was halted. The claim that marijuana impairs female reproductive functioning in humans has no support in the scientific literature. There have been no epidemiological studies indicating diminished fertility in female users of marijuana, and a recent survey found no impact of chronic marijuana use on female sex hormones. Animal studies show hormonal changes and depressed ovulation following extremely high daily doses of THC. As occurs with males, these changes disappear once the experiment is completed. In addition, when THC was administered to female monkeys for an entire year, they developed tolerance to its hormonal effects and normal cycles were reestablished. Almost immediately following publication of the few studies showing a marijuana impact on reproductive hormones, warnings about marijuana's potential impact on adolescent sexual development began to appear. Other than one case report of a 16-year old marijuana smoker who had failed to progress to puberty, there has been nothing to indicate that such a potential exists. In whatever other ways one might consider marijuana to be bad for adolescents, it does not retard their sexual development. CLAIM #7: MARIJUANA USE DURING PREGNANCY HARMS THE FETUS A powerful accusation in anti-drug campaigns is that children are permanently harmed by their mothers' use of drugs during pregnancy. Today, it is commonly claimed that marijuana is a cause of birth defects and development deficits. THE FACTS A number of studies reported low birth weight and physical abnormalities among babies exposed to marijuana in utero. However, when other factors known to affect pregnancy outcomes were controlled for-for example, maternal age, socio-economic class, and alcohol and tobacco use-the association between marijuana use and adverse fetal effects disappeared. Numerous other studies have failed to find negative impacts from marijuana exposure. However, when negative outcomes are found, they tend to be widely publicized, regardless of the quality of the study. It is now often claimed that marijuana use during pregnancy causes childhood leukemia. The basis for this claim is one study, in which 5% of the mothers of leukemic children admitted to using marijuana prior to or during pregnancy. A "control group" of mothers with normal children was then created and questioned by telephone about previous drug use. Their reported .5 percent marijuana use- rate was used to calculate a 10-fold greater risk of leukemia for children born to marijuana users. Given national surveys showing marijuana prevalence rates of at least 10%, these "control group" mothers almost certainly under-reported their drug use to strangers on the telephone. Also used as evidence of marijuana-induced fetal harm are two longitudinal studies, in which the children of marijuana users were examined repeatedly. However, on closer examination, the effects of marijuana appear to be quite minimal, if existent at all. After finding a slight deficit in visual responsiveness among marijuana-exposed newborns, no differences were found at 6 months, 12 months, 18 months, or 24 months. At age 3, the only difference (after controlling for confounding variables) was that children of "moderate" smokers had superior psycho-motor skills. At age 4, children of "heavy" marijuana users (averaging 18.7 joints/week) had lower scores on one subscale of one standardized test of verbal development. At age 6, these same children scored lower on one computerized task-that measuring "vigilance." On dozens of others scales and subscales, no differences were ever found. In another study, standardized IQ tests were administered to marijuana-exposed and unexposed 3 year-olds. Researchers found no differences in the overall scores. However, by dividing the sample by race, they found-among African- American children only-lower scores on one subscale for those exposed during the first trimester and lower scores on a different subscale for those exposed during the second trimester. Although it is sensible to advise pregnant women to abstain from using most drugs-including marijuana-the weight of scientific evidence indicates that marijuana has few adverse consequences for the developing human fetus. -- The continuing illegality of medical marijuana is based more on political than scientific considerations. 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