With regard to depression, evidence of a causal role for marijuana is even murkier. In general, depression rates in the population did rise sharply during the time period in which marijuana use also skyrocketed. But there were so many other relevant sociological factors that marked the last half of the 20th century -- rising divorce rates, the changing roles of women, economic shifts, and better diagnoses of psychiatric conditions, to name a few -- that scientists have rarely focused on marijuana as a potential cause for the increase in depression.

Murray maintains that scientists have simply overlooked marijuana in their search for explanations. One study published in the Archives of General Psychiatry in 2002, by New York University psychiatry professor Judith Brook and several colleagues, found that early marijuana use increased the risk of major depression by 19 percent. But that's not a substantial amount, according to Brook. And though the association remained after other factors were controlled for, such as living in poverty, it weakened further. "I wouldn't say that it's causal," Brook says. "It's an association. It appears to contribute."

The campaign selectively uses another piece of data, citing an Australian study published in the British Medical Journal in 2002 to assert that for teens, weekly marijuana use doubles the risk of depression. What that study found was that the risk doubled for teens who smoke marijuana weekly or more frequently. And it found that depression rates increased substantially in girls but not in boys. It also noted that "questions remain about the level of association between cannabis use and depression and anxiety and about the mechanism underpinning the link."

Moreover, a June 2005 study by researchers at University of Southern California, using the Center for Epidemiologic Studies' Depression Scale, found that marijuana use was in fact associated with lower levels of depression. Because the research was conducted using an Internet survey, it's possible that the most severely depressed people did not participate; nonetheless the study of more than 4,400 people found that both heavy pot smokers and moderate users reported less depression than did nonusers.

Dr. Myrna Weissman, a psychiatrist and leading epidemiologist of depression at Columbia University, sums up the current research and her view of marijuana's role in depression rates this way: "I can't imagine that it's a major factor."

The distortion of science under the Bush administration is, of course, nothing new.

"This is just more red-state culture-war politics," says UCLA's Kleiman, of the latest anti-marijuana campaign. He notes that since the government measures success in the war on drugs by a reduction in the number of drug users -- rather than by declines in drug-related harm or addiction -- marijuana is the obvious drug to go after. According to the most recent National Survey on Drug Use and Health from 2003, approximately 25 million Americans reported using marijuana over the previous year; compared with approximately 6 million users of cocaine and 1 million users of methamphetamine -- both far more addictive substances -- marijuana is a big, soft target.

Yet, for a public desensitized to fear-mongering antidrug messages, a campaign touting selected statistics from tenuous studies seems especially tone deaf, if not irresponsible.

"If I tell my 15-year-old that he's going to have a psychotic episode if he smokes pot, but he knows that his older brother already smokes pot and is fine, is he going to believe me when I tell him that methamphetamine damages the brain?" asks Mitch Earleywine, an associate professor of psychology at the State University of New York at Albany, who coauthored the USC study. Amphetamine psychosis is an established effect of taking large doses of that class of drugs; warnings about it appear on the labeling of prescription amphetamines. "What's going to happen," says Earleywine, "is we're going to lose all credibility with our teens."

The drug czar's office may soon face a full-blown credibility problem of its own regarding its fight against marijuana. Drug warriors have always had at least one powerful argument to fall back on when other attacks against marijuana seem to go up in smoke -- but in the face of a new study, that may no longer be the case.

Previous research has pointed to the notion that smoking marijuana could cause cancer, the same way tobacco smoking has been incontrovertibly linked with cancer and death. The Institute of Medicine, charged by Congress with settling scientific debates, said in its last major report on the subject in 1999 that the fact that most users smoke marijuana is a primary reason to oppose its use as medicine.

But that reasoning was called into question in late June, when Dr. Donald Tashkin of the UCLA School of Medicine presented a large, case-control study -- of the kind that have linked tobacco use with increases in lung cancer -- at an annual scientific meeting of the International Cannabinoid Research Society in Clearwater, Fla. Tashkin is no hippie-dippy marijuana advocate: His earlier work has been cited by the drug czar's office itself, because his research showed that marijuana can cause lung damage. The new study, however, found no connection between pot smoking -- even by heavy users -- and lung cancer. In fact, among the more than 1,200 people studied, those who had smoked marijuana, but not cigarettes, appeared to have a lower risk for lung cancer than even those who had smoked neither.

The new research has not yet been peer reviewed, but it appears congruent with earlier studies that found no link between marijuana and increased cancer risk. If the data holds up to further scrutiny and testing, one can only speculate what new ad campaign the drug czar's office might cook up. Marijuana may not make most people crazy, but this latest discovery could really drive the old drug warriors bonkers.

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