Drug Law

More Evidence Marijuana Doesn't Cause Cancer

| by Marijuana Policy Project

By Bruce Mirken

A 1999 study showed a modestly
increased risk of certain types of head and neck cancer among marijuana smokers.
Due to methodological limitations, the researchers warned that their
“results need to be interpreted with some caution in drawing causal
inferences.” But
warnings about this alleged risk have shown up from time
to time in materials put out by prohibitionist types, including the National Institute on Drug Abuse.

A new study, just published in
the journal Cancer Epidemiology, Biomarkers, & Prevention,
suggests this may have been a false alarm.

Researchers pooled data from five studies, totaling over 9,000 participants
(nearly 30 times the number in the 1999 study) and found that the risk of head
and neck cancer “was not elevated” among those who had ever smoked marijuana
compared to those who hadn’t. Notably, “there was no increasing risk associated
with increasing frequency, duration, or cumulative consumption of marijuana

The researchers note that, due to the small number of long-term, very heavy
marijuana users in the studies, they can’t rule out increased risk from such
very heavy use. But it is striking that the overall cancer risk among marijuana
smokers was slightly lower than nonsmokers, though not enough to be
statistically significant. That was also the case in a major lung cancer study a few
years ago. In the new study, there were some subcategories in which the lowered
risk among marijuana smokers came close to statistical significance.

But don’t expect mere data to put an end to hysterical claims that marijuana is more
carcinogenic than tobacco.