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What are the long term health effects of marijuana?

Dear Cecil:

It's time us smokers, tokers, and dopers heard the Straight Dope on … you guessed it … dope! As you know, apathy and lack of ambition are alleged to be the fate of all consumers of the evil weed. However, though I have been smoking for years, I have no lack of ambition, and in fact could be considered quite successful. I know many other marijuana smokers about whom one could say the same thing. What's the scoop? And what are the other long-term effects of marijuana usage, i.e., what are we doing to our lungs, brains, blood, and what have you?

N. R., Phoenix

Illustration by Slug Signorino

Cecil replies:

(Column updated 1997; also see 2006 update on the subject posted here.)

Well, we’ve now established that marijuana won’t prevent you from becoming president, provided you don’t inhale. As for other effects, a major review, Marijuana and Health, was issued in 1982 by a panel of scientists working for the National Academy of Sciences. Subsequent research has done little to alter their conclusions. Here’s what they said:

The “amotivational syndrome” (i.e., apathy). Sure enough, dopers tend to be apathetic. But it’s never been proven that marijuana causes apathy. In fact, the panel found, it may well be the other way around — maybe apathy causes you to use marijuana. On a related subject, the panel noted that atrophy in the brains of 10 heavy marijuana users had been reported some years ago by a British researcher. Another scientist at Tulane said he found “dramatic” changes in the brains of monkeys subjected to carloads of cannabis. But both studies were sharply criticized for methodological deficiencies. Other scientists have found no brain damage. This led the NAS panel to conclude, predictably, that “much more work is needed.” A 1995 review of marijuana’s effect on the brain said pretty much the same thing and as far as I can tell the question remains unsettled today. As for “reefer madness,” there is little evidence that marijuana per se causes psychosis, but it may trigger psychotic episodes in people who have mental problems to start with.

Lungs. Marijuana smoke contains about 50 percent more carcinogenic hydrocarbons than cigarette smoke. Tests with lab animals and whatnot indicate that marijuana-induced lung cancer is a real possibility. (They also indicate that smoking both marijuana and tobacco is worse than smoking just one or the other.) Still, as of 1982, there had never been a case of lung cancer attributable solely to dope smoking — possibly, according to the panel, “because marijuana has been widely smoked in this country for only about 20 years, and data have not been collected systematically in other countries with a much longer history” of heavy dope use. A somewhat alarmist 1992 report from Australia claimed that marijuana had been implicated in cases of mouth, jaw, tongue, and lung cancer. I’m skeptical of claims that marijuana was the sole cause of these cancers, however. Even if one assumes the worst, marijuana as a carcinogen pales in comparison to tobacco. Be that as it may, heavy dope users are prone to respiratory problems such as pharyngitis, sinusitis, bronchitis, and asthma.

Heart. Dope smoking places extra stress on the heart, the panel said. This is probably harmless to healthy people, but if you have high blood pressure or hardening of the arteries, or if you’re prone to strokes, you should lay off.

Reproductive system. Dope suppresses the production of male sex hormone, shrinks the testes, and inhibits sperm production. Fortunately, the effects don’t seem to be permanent. Animal studies indicate that marijuana also inhibits ovulation in females. Dope does not cause chromosome damage. As of 1982 there was no hard evidence that it caused birth defects or low birth weight and from what I can see there still isn’t.

Finally, there’s no question that smoking does make you, well, stoned — i.e., it’s harder to concentrate, your coordination deteriorates, and so on. If you smoke during lunch hour your job performance will suffer. In addition, the panel says, your abilities remain impaired for four to eight hours after the feeling of being stoned passes — much longer than with alcohol. So don’t smoke if you’re going to drive or do any sort of complex task later in the day.

There are still a few people who think marijuana is a major health threat. But the more common view is that, while marijuana doesn’t exactly qualify as health food, on the whole it causes fewer problems than its two main competitors on the recreational drug scene, alcohol and tobacco. Granted, that’s like saying it causes fewer problems than nuclear war. But you do have to ask why marijuana is illegal and alcohol and tobacco aren’t.

Cecil Adams

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