Everyone knows that smoking isn't good for you - no matter what's in the cigarette. But a new study out of New Zealand shows those who indulge in even the occasional marijuana joint may be elevating their risk for lung cancer in a dangerous way.

Doctors at the Medical Research Institute of New Zealand have concluded smoking a single joint is equivalent to inhaling the damaging contents of 20 regular tobacco cigarettes. And they're now worried about what they call a potential "epidemic" of lung cancer patients in current and future generations.

It's not the first time research has made a link between smoking pot and the often fatal disease. But it's the first one to so definitively declare the danger and put it so far above any other kind of smoking.

The scientists found cannabis contains twice the level of carcinogens that regular butts do. And the fact joints don't come with actual filters only magnifies the problem. Pot smokers also tend to hold the smoke in longer to enhance the effect of the drug in their systems and they tend to burn their self-made roll-your-owns right down to the end.

"Cannabis smokers end up with five times more carbon monoxide in their bloodstream (than tobacco smokers)," team leader Richard Beasley relates. "There are higher concentrations of carcinogens in cannabis smoke ... what is intriguing to us is there is so little work done on cannabis when there is so much done on tobacco."

The doctors studied 79 lung cancer patients in an attempt to find out what their greatest risk factors were for getting the ailment. The subjects were asked how much they smoked and drank, what their family histories were, what they did for a living and exactly how much of each substance they consumed.

The results were telling. The cancer rates for those who admitted smoking a single joint a day for a decade or two over a five year period soared - even taking regular cigarette use into account.

Many pot advocates have decried this kind of research in the past, arguing it's simply a scare tactic to discourage their use of the product. But the study authors say they're not trying to convey an anti-drug message so much as a pro-health one.

And in a present where the pressure on the health care system is already intense, many are worried about what it may mean going forward.

"In the near future we may see an 'epidemic' of lung cancers connected with this new carcinogen," warns Beasley. "And the future risk probably applies to many other countries, where increasing use of cannabis among young adults and adolescents is becoming a major public health problem."