Could smoking marijuana increase the risk of developing cancer? This controversial question has been raised by the first study to investigate a possible link between cannabis use and testicular cancer. A group at Fred Hutchinson Cancer Research Center, USA, interviewed men with testicular cancer about their history of cannabis use, and found that being a regular cannabis smoker at the time of diagnosis conferred a 70% increase in risk. Even after accounting for other lifestyle factors, such as smoking and drinking, cannabis was still a significant risk factor.

The authors discovered a link between cannabis use and aggressive non-seminoma-type testicular cancers, which account for ∼40% of all cases and typically strike men in their 20s and 30s. Dr Janet Daling, one of the authors of the study, suggests that puberty could provide a “window of opportunity” in which boys could be more susceptible to environmental factors, such as the chemicals present in cannabis, and that “this is consistent with the study's findings that the elevated risk of non-seminoma-type testicular cancer in particular was associated with marijuana use prior to 18” (The Independent, 9 Feb 2009).

“In the absence of more certain information, a decision to smoke marijuana recreationally means that one is taking a chance on one's future health,” said Dr Stephen Schwartz, the leader of the study (The Telegraph, 9 Feb 2009). However, further studies are required before any definitive conclusions can be drawn. Henry Scowcroft, from Cancer Research UK, said, “[T]he researchers only interviewed a relatively small number of men. So before we can reach any firm conclusions about whether this is a cause-and-effect relationship, rather than a statistical blip, the result needs to be replicated in a much larger study” (BBC News, 9 Feb 2009). These findings certainly add further fuel to the debate over the potential risks of cannabis use.