AN increased risk of developing testicular cancer from smoking marijuana is just one more reason not to use the drug, Australian researchers say.

An American study published in the journal Cancer compared 163 young men diagnosed with testicular cancer with about 290 healthy men of the same age.

It found that men with a history of recreational marijuana use were twice as likely to have two types of testicular cancer that commonly occur in younger men and carry a worse prognosis.

The findings confirmed earlier studies which also showed links between cannabis use and testicular cancer.

The founding professor and director of the National Cannabis Prevention and Information Centre (NCPIC) at the University of NSW, Jan Copeland, said the results were not surprising because there were cannabis receptors in the testes and smoking marijuana affected sperm development.

"It is just one more avoidable risk factor for the development of a range of health conditions," Professor Copeland said.

"As the peak ages for the development of testicular cancer and cannabis use coincide in young adulthood, protecting health and fertility is just one more reason not to smoke cannabis for this high-risk group."

Cancer Council Australia CEO Ian Olver said although studies that relied on self-reporting drug use could be questionable, the results of this study were convincing.

The study also found that men with a history of cocaine use had a reduced risk of both subtypes of testicular cancer.

The University of Southern California study suggested this could be because cocaine had already damaged or killed sperm-producing germ cells, therefore those cells could not become cancerous.

Marijuana use has previously been linked to and increased risk of schizophrenia, memory loss and learning difficulties,