Recreational Marijuana: Are There Health Effects?

Dec. 11, 2012 -- On Monday, Colorado Gov. John Hickenlooper signed an order legalizing recreational marijuana use for adults.

Last week, Washington was the first state to OK adult recreational use of the drug. Several other states are considering similar laws.

While much research has focused on the value of medical marijuana to help chronic pain and other problems, what about the health effects of purely recreational marijuana?

WebMD turned to two experts, recently published studies, and the National Institute on Drug Abuse to draw up a scorecard of possible major health effects.

"Putting smoke in your lungs is not good for the lungs," says Roland Lamarine, HSD, professor of public health at California State University, Chico. He reviewed published studies on the health effects of marijuana earlier this year for the Journal of Drug Education.

Smoking marijuana produces a nearly threefold increase of inhaled tar compared with tobacco, according to some studies. Other research suggests that marijuana smokers, compared to cigarette smokers, inhale more deeply and hold their breath longer.

"There are still questions that aren't answered about lung damage," Lamarine says. For cigarette smokers who also smoke marijuana, there may be an additive effect, he says.

Combining the two appears to be a trend, he says. "Some of the [college] kids tell me they buy cigars and put in some marijuana, so there is both marijuana and tobacco," Lamarine says.

Marijuana smoke contains cancer-causing substances, according to the National Institute on Drug Abuse. Some research shows that marijuana smoke has up to 70% more cancer-causing substances than tobacco smoke, it says.

"Nobody is advocating that routinely inhaling carcinogenic smoke is healthy," says Paul Armentano, the deputy director of NORML (National Organization for the Reform of Marijuana Laws).

However, he says, many marijuana users these days have turned to alternate delivery methods, such as oral, tinctures, and vapor forms. In research, he says, the vaporized forms have fewer adverse chemicals than the inhaled form.

Those who keep marijuana use light do not appear to lose lung function, according to a 2012 study in the Journal of the American Medical Association.

Researchers compared tobacco and marijuana users. Tobacco use was associated with lower lung function, and the function got worse as smoking levels increased.

For the study, low levels of lifetime exposure to marijuana, defined as one joint a day for seven years, did not show evidence of adverse effects on lung function. The study does not confirm these findings with heavy users.

Long-term, heavy use of marijuana can lead to impaired thinking skills and memory problems, Lamarine says, citing published studies.

The impairments can be especially hazardous when trying to do everyday activities such as driving.

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