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Reply to 'Marijuana, the Deceptive Drug'
Biernson’s review of the evidence on marijuana’s effects is highly skewed

We requested Prof. Jeffrey A. Miron to reply to the article which appeared in our last issue about the dangers of marijuana. Prof. Miron is the founder of the Bastiat Institute, a libertarian think tank in Wellesley and a professor at Boston University. Needless to say, the author of the original article, George Biernson and others, are anxious to reply to Prof. Miron in our next issue. We hope this exchange will allow you to sharpen your views on the subject.

Massachusetts News
By Jeffrey A. Miron

February 1--In Marijuana, the Deceptive Drug, which appeared one month ago in this newspaper, George Biernson argues that marijuana is a dangerous drug, more dangerous than heroin, cocaine, alcohol or tobacco. Biernson claims, in particular, that regular marijuana use substantially damages the brain, the immune system, the reproductive system, and the lungs. He also suggests that regular marijuana smoking causes sedation and confusion, implying these effects can persist for more than a month after the use of marijuana. Biernson also asserts that marijuana is a "gateway drug’’ – meaning its use encourages a progression toward other drugs like cocaine or heroin – and he implies that marijuana use causes crime.

Biernson’s conclusions are based on his reading of the scientific literature that examines the medical and other effects of marijuana. This literature is vast, and it contains at least one or two studies that appear to support almost any view. Yet all scientific studies are not created equal. Some employ careful controls, use appropriate statistical techniques, and are easily replicated by independent researchers. Many other studies are poorly controlled, employ problematic statistical methods, or fail to be replicated by subsequent research. An objective assessment of the evidence, therefore, must consider all the evidence, and it must attempt to place greater weight on well-designed, carefully interpreted, and easily replicated studies than on those that do not satisfy these standards.

Highly Skewed

My contention is that Biernson’s review of the evidence on marijuana’s effects is highly skewed. The pages of this newspaper are not an appropriate forum in which to debate the merits of the individual studies cited by Biernson in the longer work on which he based his article, nor is it possible to present here the vast array of research findings that reaches substantially different conclusions from those suggested by Biernson. What I attempt, instead, is to show the reader that alternative reviews of the evidence have reached strikingly different conclusions than Biernson’s. Moreover, even without recourse to the scientific literature, thoughtful consideration of Biernson’s assertions should leave the reader skeptical regarding the more extreme claims made in his article.

A first alternative assessment of the evidence is provided in Goodman & Gilman’s The Pharmacological Basis of Therapeutics, Ninth Edition (1996), which is the standard reference work on basic pharmacology. The editors of this text are an associate vice-chancellor of the Vanderbilt University School of Medicine, a chairman of the Department of Pharmacology at the Vanderbilt School of Medicine, a chairman of the Department of Pharmacology at the University of Pennsylvania School of Medicine, a director of the cancer center at the University of Nebraska Medical Center, and a chairman of the Department of Pharmacology at the University of Texas Southwestern Medical Center. The authors of the various chapters in the volume include professors at most of the elite universities and medical centers in the United States, including Harvard, Stanford, Duke, Virginia, Michigan, and Pennsylvania, amongst others; the author of the section on marijuana is Chief of Psychiatry, Veterans Administration Medical Center, and Professor and Vice-Chairman of Psychiatry, at the University of Pennsylvania School of Medicine.

The portion of this text that discusses marijuana says that "there is no evidence that marijuana use damages brain cells or produces any permanent functional changes.’’ Regarding the claims that marijuana smoking makes users confused or sedated, it states that "there are no data that demonstrate a causal relationship between marijuana smoking and these behavioral characteristics.’’ The text also notes that relatively few patients ever seek treatment for marijuana addiction.

Not Harmful

A different assessment of the evidence on marijuana comes from Lester Grinspoon and James B. Bakalar, associate professor of psychiatry and lecturer in law, respectively, in the Department of Psychiatry at Harvard Medical School. In their 1997 book, Marihuana, The Forbidden Medicine, they write that "after carefully monitoring the literature for more than two decades, we have concluded that the only well-confirmed deleterious physical effect of marihuana is harm to the pulmonary system.’’ As they note, moreover, even this effect can be minimized by the use of high potency marijuana (which means relatively little marijuana need be smoked) or by means of filtering devices, as occurs with cigarettes. In the introduction, Grinspoon notes that when he began studying marijuana, several decades ago, he was convinced it was a harmful drug, and he aimed to document those dangers scientifically. Yet upon reviewing the evidence he concluded that marijuana was "considerably less harmful than tobacco and alcohol.’’

New Evidence

The most recent comprehensive review of the evidence is provided in the 1997 book Marijuana Myths, Marijuana Facts, by Lynn Zimmer and John P. Morgan. Zimmer is an associate professor of sociology at Queens College of the City University of New York, and Morgan is a professor of pharmacology at the City University of New York and an adjunct professor of pharmacology at the Mount Sinai School of Medicine. They review most if not all of the marijuana studies cited by Biernson; but they also consider hundreds of other studies, many of which explicitly reply to those Biernson relies on. 

According to Zimmer and Morgan, some of the studies cited by Biernson have been flatly contradicted by subsequent work; in other cases these studies suffer from poor research designs, small samples, or inapplicability to humans. And more generally, they are but a small portion of the available evidence, most of which reaches substantially different conclusions. With respect to every claim made by Biernson – regarding health, addiction, gateway effects, psychological damage, criminogenic effects, and the like – as well as with respect to numerous other issues, Zimmer and Morgan conclude that marijuana’s negative effects have been drastically exaggerated, and that in most cases there is little evidence of any harm even from regular marijuana use. They note that their evaluation is simply the most recent in a long line conducted in the United States and elsewhere, including the Indian Hemp Drugs Commission (1894), the Panama Canal Zone Report (1925), the LaGuardia Commission Report (1944), the British Wooten Report (1969), the Canadian LeDain Commission Report (1970), the National Commission on Marihuana and Drug Abuse (1972), the Dutch Baan Commission (1972), the Commission of the Australian Government (1977), the National Academy of Sciences Report (1982), and the Report by the Dutch Government (1995). All these reviews of the evidence find that marijuana’s harms have been highly exaggerated and conclude that moderate, responsible use poses little demonstrable risk.

Beyond the fact that numerous, reputable experts have drawn radically different conclusions than Biernson from reviews of the evidence on marijuana, a further fact to consider is the large amount of marijuana consumption that occurs in the United States every year. According to government surveys, approximately 72 million Americans have used marijuana in their lifetime, and more than 18 million have used it recently. These numbers plausibly understate the true number of persons with marijuana experience, since many persons are plausibly reluctant to admit illegal behavior to government surveys. If Biernson’s claims about addiction or gateway effects are even partially accurate, we ought to observe a large fraction of those who try marijuana becoming regular users, and a substantial fraction of these users progressing to cocaine or heroin use. Similarly, if Biernson’s’s claims about marijuana’s health, or psychological, or criminogenic effects are accurate, we ought to observe inordinate numbers of teenagers exhibiting a motivational syndrome and committing large numbers of crimes, as well as legions of patients presenting with marijuana-induced ailments. Yet none of these implications has any basis in fact. Most of those who try marijuana, or who use it occasionally, stop using it of their own volition, without serious difficulty. Only a small fraction of those who use marijuana ever try cocaine or heroin, let alone become regular consumers of these drugs. And any "epidemic’’ of marijuana-induced ailments is simply nonexistent.

Not Harmless

None of this evidence, it must be emphasized, shows that marijuana is harmless; indeed, several of the scientific reviews cited above note explicitly the possibility that marijuana smoking causes lung damage, and they note the possibility (as yet not convincingly documented) that marijuana use during pregnancy has adverse effects on the fetus. These scientific reviews also note that marijuana use can impair the ability to drive a car or perform other complex tasks (although several studies find a larger negative effect of alcohol on driving ability and other activities). Thus, these reviews are not necessarily endorsements of marijuana or suggestions that it can be consumed without risk by all persons under any circumstances. But these reviews paint a far different picture than the one suggested by Biernson. Moreover, they are written by authors with credentials at least the equal of those cited by Biernson, and they are based on far more extensive and recent reviews of the evidence.

One reason for the different assessments of the evidence, especially the evidence of sociological or criminogenic effects of marijuana, is the difficulty in distinguishing cause from effect. The set of persons that chooses to use drugs is not likely to be a random sample of the population, and this has key implications for interpreting correlations between marijuana use and other kinds of behavior. Thus, a finding that marijuana users are unmotivated or underachieving, or prone to psychological difficulties, or the like, does not demonstrate that marijuana causes these phenomena. Any evidence of such a correlation might instead suggest that the decision to use marijuana results from emotional difficulties or more serious psychological problems, including ones that have yet to manifest openly. Similarly, the fact that a substantial fraction of those arrested have consumed marijuana does not demonstrate a causal effect of marijuana use on criminality, any more than the fact that most arrested persons wear blue jeans shows denim causes criminality. Instead, the correlation between marijuana use and criminal behavior plausibly reflects the fact that certain types of people are both prone to consume marijuana and to commit crime, without any causal relation.

Biernson’s Response?

A possible response that Biernson might make to these arguments, even if he were to accept this milder assessment of marijuana’s effects, is that marijuana is still dangerous because it leads to consumption of other dangerous substances, such as cocaine or marijuana (the so-called "gateway,’’ or "stepping-stone’’ effect). One important response to this argument is the fact that, although by no means without risks, cocaine and opiate consumption are also far less dangerous than commonly portrayed, and can themselves be consumed without substantial harm even over long periods. Many of the hazards associated with cocaine and opiate consumption result from their prohibition, which encourages users to accept uncertain quality, pay higher prices, purchase drugs from potentially violent criminals, and employ risky administration techniques that can transmit HIV or other infectious diseases.

But whether or not one accepts this point, the claim of a gateway effect for marijuana is problematic and unsubstantiated. It is true that most users of cocaine and opiates consumed marijuana before consuming these other drugs, just as they consumed alcohol in most cases before consuming marijuana. But these same persons also consumed french fries before they consumed alcohol, and milk before they consumed french fries; the temporal sequencing of different kinds of consumption does not mean that one causes the other. The vast majority of those who use marijuana do not go on to other drugs, so any gateway effect is small at best. Moreover, exaggerating marijuana’s health effects might encourage a gateway effect. When teenagers are told that marijuana is dangerous, but inevitably find out this claim is misleading, they conclude (correctly) that adults are lying about marijuana. This can only encourage them to think the claims about cocaine or heroin are manufactured as well (which they are to a substantial degree), and thus make them more likely to experiment further.

A balanced review of the evidence, therefore, suggests a far more nuanced picture of marijuana than suggested by Biernson. To repeat, this does not mean marijuana is risk free; but no substance is safe for all persons, or under all circumstances, or in arbitrarily high doses. Common over the counter medications, such as aspirin, cause hundreds of deaths per year; common foods, such as peanuts, or medications such as penicillin, readily kill persons who are allergic. And the treatments for many diseases, such as chemotherapy for cancer, can easily cause death in doses only modestly above the clinically recommended amounts. Tobacco, alcohol and saturated fats all cause disease or death under some circumstances, as do automobiles, swimming pools, and children’s toys.

The relevant question for consumers of any commodity, therefore, is whether the benefits outweigh the potential harms. Biernson’s characterization of marijuana’s effects is meant to suggest that the harms from marijuana are so great that no person who understood these harms would ever voluntarily consume marijuana. That characterization is not consistent with an objective assessment of the evidence.


1. Grinspoon, Lester and James B. Bakalar (1997), Marihuana, The Forbidden Medicine, New Haven: Yale University Press.

2. Hardman, Joel G., Lee E. Limbird, Perry B. Molinoff, Raymond W. Ruddon, and Alfred Goodman Gilman, eds. (1996), Goodman & Gilman’s The Pharmacological Basis of Therapeutics, Ninth Edition, New York: McGraw-Hill. 

3. Lynn and John P. Morgan (1997), Marijuana Myths, Marijuana Facts, New York: The Lindesmith Center.

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