Many cancer patients use marijuana and its usage has increased, a new study suggests. The findings, published in the journal CANCER, indicate 40.3 percent of cancer patients used marijuana within the past year, compared with 38 percent of respondents without cancer.

"Prospective clinical trials are needed to quantify the efficacy of marijuana in cancer-specific pain as well as the risk of opioid misuse in this patient population," said co-author Kathryn Ries Tringale from the University of California, San Diego.