Scientists think they may have found a link between the frequent use of cannabis and incidents of testicular cancer.
The study, by the Fred Hutchinson Cancer Research Centre in the USA, looked at 369 men with testicular cancer and discovered that being a marijuana smoker at the time of diagnosis was associated with a 70% increased risk.
Those who used the drug at least once a week or had long-term exposure to the substance starting from adolescence had a risk factor of about twice that of those who had never smoked marijuana.
The results, published online the journal Cancer, found that frequent use of the drug might only be associated with a fast-growing type of the disease which tends to strike early, aged between 20 and 35, known as nonseminoma. This accounts for about 40% of all cases.
Researchers were alerted to a possible association between the drug and the disease when they noticed that since the 1950s, the incidence of two types of testicular cancer had increased by 3–6% in the USA, Canada, Europe, Australia and New Zealand - with marijuana use rising accordingly.
Researchers emphasised that their results were not definitive, and should lead to more research questions.