But cocaine use can reduce the risk by half.
These are just some of the conclusions a team of researchers at the University of Southern California came to after interviewing more than 350 men, 163 of whom had been diagnosed with testicular cancer, about recreational drug use.
"We do not know what marijuana triggers in the testes that may lead to carcinogenesis, although we speculate that it may be acting through... the cellular network that responds to the active ingredient in marijuana, since this system has been shown to be important in the formation of sperm," said Victoria Cortessis, lead author and assistant professor of preventive medicine at USC's Keck School of Medicine.
The questionnaire included entries for poppers, mushrooms, Quaaludes, PCP, barbiturates and speed. Testicular cancers are the most common forms of cancer in adolescent and adult men between the ages of 15 and 45, Cortessis said. The research appeared in today's edition of the journal Cancer.
The number of men getting testicular cancer has been on the rise, Cortessis said, indicating something other than genetics is playing a role. Researchers have speculated that chemicals affecting the hormone system could be partly responsible, including some of the properties found in marijuana smoke.
"This isn't the first time that this information has come out," said Michael Craycraft, testicular cancer survivor and founder of the Testicular Cancer Society, a support and advocacy group for men and boys diagnosed with the disease.
"There have been at least two other studies in the past couple of years that have basically shown the same thing," he said. "In particular, that marijuana smoking is associated with nonseminoma, a harder-to-treat kind of testicular cancer."
Cortessis' group found the same thing: It was this hard-to-treat variety of testicular cancer that appeared most prevalent in these men.
The cocaine association the team found was surprising, and harder to explain. In the research paper, the scientists stressed that the drug should not be used as a preventative measure.
Indeed, they speculate that cocaine's effects on the testes are probably not ones that most men would condone, or any physician would support. As the authors write about cocaine's effects on rat testes: "Spermatogenesis is rapidly disrupted accompanied by cell sloughing and reduction in testicular volume."
And they note, another explanation could be as simple as cocaine's effects on veins: It shrinks them. Therefore, the drug is squeezing out the blood supply to the testes and making it impossible for them to produce cells.
In any case, they note, marijuana, cocaine and other recreational drugs should probably be avoided.
Parents should talk to their teens about the potential side effects of marijuana, Craycraft said, adding that anyone who did smoke pot as a teen should be extra vigilant about cancer.
Read more California investigative reports at CaliforniaWatch.org.