We knew marijuana had the ability to impair male fertility -- making it harder for heavy tokers to get their swimmers moving. Now it seems there's another serious risk for stoners to consider.

Scientists have found that heavy pot smoking can double a guy's risk of testicular cancer. The disease is currently on the rise in Western countries, and researchers link it to an uptick in people smoking dope. The study looked at the habits of 369 men with testicular cancer and compared them to guys who didn't have the disease. Chances of contracting the disease were particularly increased when smokers started hitting the pipe before the age of 18.

The testes are among the parts of the body with receptors for tetrahydrocannabinol (THC) -- the psychoactive ingredient in pot -- and they also produce a cannabis-like chemical that scientists think protects against cancer. The theory is that if you smoke too much pot, it interferes with your body's natural ability to protect against the disease.

In related news, the next Cheech and Chong movie will be a heart-wrenching melodrama about the power of male friendship in the face of overwhelming odds.