According to American research frequent and regular use of cannabis can lead to as much as a 70 % increased risk of testicular cancer.

The incidence of testicular cancer has risen in the UK and other Western countries to more than double over the past 30 years and this rise is reflected in the increase in popularity of cannabis which is dubbed as Britain's most popular illegal drug.

The study from scientists at the Fred Hutchinson Cancer Research Center in Seattle is the first to look specifically at marijuana use in relation to the disease and was conducted on 369 men aged 18 to 44 with testicular cancer who were questioned about their history of cannabis use. The results were matched to those of 979 men who did not have cancer. The researchers found that regular users of the drug doubled the risk of testicular cancer in men as compared to men who had never smoked it.

The risk was found to be the highest in those who smoked it at least once a week or were regular users for a long period of time, beginning in adolescence. The link between cannabis and testicular cancer was independent of smoking, drinking and family history, other known risk factors for testicular cancer.

The researchers said just being a marijuana smoker carried a 70% increased risk and a link was found between nonseminoma, a fast-growing form of testicular cancer which accounts for approximately 40% of all cases, and tends to strike younger.

This is an aggressive form of cancer which is one of the most common in younger men and approximately 2,000 new cases are detected each year in the UK. The steady rise of the cancer is seen to be higher in Europe and North America than in other parts of the world though experts don't know why.

Dr Janet Daling, one of the authors of the study said that puberty might carry a link as in this period boys were more vulnerable to environmental factors such as the chemicals in marijuana. "This is consistent with the study's findings that the elevated risk of nonseminoma-type testicular cancer in particular was associated with marijuana use prior to 18," she said.

Previous injuries to the testicles, a family history of the disease, or suffering from undescended testicles as a young child are some of the factors that are known to increase the risk of testicular cancer.

Henry Scowcroft, from Cancer Research UK said, "As the researchers themselves point out, this is the first inkling that there is any association between chronic marijuana use and testicular cancer.

"But the 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."

A spokesman for Cancer Research UK said that no previous studies had found a link between marijuana and the disease.