Marijuana smoke, like tobacco smoke, contains many carcinogens. Researchers in Seattle looked at whether it increases the risk of oral cancer.

What the researchers wanted to know: Does smoking marijuana increase the risk for oral cancer?

What they did: The researchers used 407 people between 18 and 65 years old who lived in one of three counties around Puget Sound, in Washington State, and had been diagnosed with oral squamous cell carcinoma—oral cancer. They also used random-digit dialing to find a group of people the same age and sex as the cancer patients, for comparison. Each patient and control was interviewed in person about his marijuana, hashish, tobacco, and alcohol use. The idea was to see whether people with oral cancer were more likely to have used marijuana than people who didn't have oral cancer.

What they found: Smoking marijuana had no discernible effect on oral cancer risk. Drinking alcohol and smoking tobacco did increase oral cancer risk. About a quarter of the patients and a quarter of controls had ever used marijuana.

What the study means to you: There may be plenty of reasons not to smoke marijuana—jail time, for example, or other cancers—but oral cancer risk doesn't seem to be one of them.

Caveats: Slightly fewer than 60 percent of people contacted agreed to take part in the study, and it's easy to imagine that people who used marijuana would be more likely to refuse to participate. Also, people might have lied about their illegal drug use.

Read the article: Rosenblatt, K.A. et al. "Marijuana Use and Risk of Oral Squamous Cell Carcinoma." Cancer Research. June 1, 2004, Vol. 64, pp. 4049–4054.

Abstract online: http://cancerres.aacrjournals.org