It's no secret that marijuana makes people high. But can it also send them six feet under?

That's the crux of an ongoing debate in the latest issue of the British Medical Journal between experts who disagree about the potential health risks of smoking pot.

The latest volley in the battle came this month, when an American doctor took aim at suggestions by a British team that marijuana could be a major killer.

'I don't think it [marijuana] contributes very much to people dying. It's not in the league of alcohol or tobacco,' says Dr. Stephen Sidney, an associate director of clinical research with the Kaiser Permanente health plan who has studied the effects of marijuana use on life span.

The debate began in May, when the journal ran an editorial by a British medical professor and colleagues suggesting the United Kingdom isn't paying enough attention to the health risks of marijuana.

'We were concerned that smoking is constantly being regarded as a major public health hazard, while cannabis, which is also usually smoked rather than consumed any other way, seems to have been completely overlooked,' says Dr. John A. Henry, a professor at the Imperial College School of Medicine at St Mary's Hospital in London.

Tobacco smoking kills almost 1 percent of smokers each year in the United Kingdom, and if marijuana had the same effect, some 30,000 people would die from it annually, Henry and colleagues wrote.

'Even if the number of deaths attributable to cannabis turned out to be a fraction of that figure, smoking cannabis [marijuana] would still be a major public health hazard,' the team wrote.

Studies Debunk Pot-Death Connection

The suggestions in the editorial spawned a flurry of letters and commentaries. In the most recent one, printed in the Sept. 20 issue of the British Medical Journal, Sidney points to two studies that debunked any connection between marijuana and higher death rates.

In a Swedish study, researchers found no link between marijuana use among more than 45,000 male military conscripts, aged 18 to 20, and their death rates over the next 15 years.

Another study of 65,171 men and women enrolled in the Kaiser Permanente health plan found that, with the exception of AIDS patients, marijuana users were not more likely than others to die over a 10-year period.

Sidney acknowledges the follow-up periods are short, and says the marijuana users in the studies could still suffer from higher rates of disease later in life.

Even so, evidence suggests smoking pot is much safer than smoking cigarettes, he says. 'One of the reasons is that marijuana is not inherently as addictive as tobacco because it doesn't contain nicotine. Many more people get addicted to tobacco smoking than marijuana smoking.'

Also, pot users take much less smoke into their lungs than tobacco users, and many stop using marijuana as they get older, Sidney says. 'It's the unusual person who's smoking seven marijuana cigarettes or joints a day. They're not smoking more than one on average, and they tend to quit.'

Substance May Contribute to Mental Illness

Some studies have linked marijuana use to a variety of medical problems, including schizophrenia, head and neck cancer and lung cancer, but the research isn't conclusive, Sidney says. There's also evidence that suggests people with heart disease should be careful about smoking pot.

What to do? 'There are common-sense measures about using marijuana,' Sidney suggests. 'It should be discouraged in teenagers. Young teenagers getting involved in drugs are going to have more of a problem with it. And people ought not to be driving around in cars and operating dangerous machinery when they're intoxicated with anything.'

On the other side of the debate, Henry wants to see more prevention efforts, if only because pot smoking may contribute to mental illnesses such as schizophrenia.

'This alone is sufficient for a public health campaign, given the disabling nature of the disorder for the individual and the massive public health burden it imposes on society,' he says.