A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Still smokin': What are the long-term effects of marijuana?

April 14, 2006

Dear Cecil:

Though far from being an all-out pothead, I occasionally smoke a little smoke and, to the best of my knowledge, have never experienced any ill effects (aside from that way natty brownie I ate on my 18th birthday). I have however heard a ton of nonsense on the subject concerning brain cancer, sterility, mental disorders, and, thanks to one fanatically religious friend, death and damnation. Being a reasonably health-conscious guy, I was wondering, what serious physical or mental effects could smoking marijuana have on me?

I first wrote about the health implications of pot use in 1985. See (The Straight Dope: What are the long term health effects of marijuana? ) Short version: Won't kill you, but ain't mother's milk either.) Since then a staggering amount of research has been done--a search on marijuana in PubMed, the federally funded online medical-journal database, turns up close to 4,000 articles in the last ten years alone. Start reading up on the subject, though, and you quickly realize that however fine the wheels of science may grind, they sure grind exceeding slow. Believe it or not, some of these guys are still arguing over whether weed causes reefer madness. The latest:

Does marijuana cause "cannabis psychosis"? The classic horror story from the early days of the antimarijuana campaign was that smoke would turn you into a frothing maniac. In college we all thought this was pretty comical. Fact is, however, that smoking large amounts of potent marijuana makes some people go nuts. One study (Chopra and Smith, 1974) told of 200 Calcutta psychiatric patients hospitalized in the 60s for psychotic symptoms after major herb intake, including hallucinations, amnesia, paranoia, etc. The question remains, however, whether dope (a) merely triggers or exacerbates psychosis in people having some genetic or other predisposition thereto, or (b) causes otherwise perfectly healthy folks to flip out. In a 2004 review Australian psychologist Wayne Hall and associates argue that "evidence for there being a distinct 'cannabis psychosis' is weak." (One argument against: the absence of a schizophrenia epidemic despite increased marijuana use.) Other researchers still hotly insist that dope is, or anyway might be, a mental-health menace. I'm not claiming things have gotten to the level of Shiites vs. Sunnis yet, but professional opinion is definitely splitting into two camps. This brings us to a related subject:

Is marijuana good for you? Twenty years ago the realist's view of pot was that, despite what 60s romantics liked to think, the stuff in some ways combined the worst features of alcohol and tobacco: it could get you dangerously wasted, and it might cause lung cancer. That attitude has now been tempered by two related developments: first, a greater appreciation of the usefulness of marijuana in treating glaucoma, multiple sclerosis, epilepsy, appetite loss in cancer and AIDS patients, and other conditions; and second, the discovery of endocannabinoids, the cannabislike chemicals that perform important regulatory functions in the body. Cannabis research is now a thriving industry, giving rise to pronouncements not far removed from what you used to hear back in the days of love beads, e.g., "the endocannabinoid system [may be] nothing less than [the body's] naturally evolved harm reduction system" (Melamede, 2005).

Does marijuana cause memory loss, apathy, etc? While these questions haven't been settled (big surprise), scientific fans of cannabis now put a different spin on them. Getting stoned makes you forgetful? Hey, that's not a bug, it's a feature. Biologist Robert Melamede, author of the article cited above, writes, "Cannabinoids control the extinction of painful memories. What a blessing for those suffering from debilitating or life threatening illnesses: cannabinoids may help them to forget their misfortune." Cannabinoids also regulate nerve sensitivity, preventing early cell death due to overexcitement--in other words, they make cells mellow out much as they do the whole organism.

So what about pot and cancer? Couple points. (1) While smoking inevitably introduces stuff into the lungs that isn't doing you any good, there's reason to believe that cannabis, unlike nicotine, may not be inherently carcinogenic--at any rate, it doesn't cause the kinds of cancer tobacco does (Sidney et al, 1997). (2) Marijuana not only helps alleviate some side effects of cancer treatment, conceivably it can fight cancer itself. Research suggests cannabinoids kill cancerous cells in cases of leukemia, lymphoma, breast and prostate cancer, etc.

Other issues quickly noted. All I see about marijuana and brain cancer is a study linking brain tumors in children to marijuana exposure during pregnancy--the link was said to be of "borderline significance." Dope's impact on fertility, meanwhile, remains controversial. As I said, we haven't made much progress pinning down the facts about what the Eagles liked to call colitas. But we're definitely seeing the emergence of a different point of view.

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