Patients undergoing chemotherapy report that medical marijuana relieves spasms, promotes appetite, and reduces nausea and vomiting.

Marinol, a synthetic cannabis drug prescribed to treat nausea, does not contain the other ingredients of whole-plant cannabis that reduce side effects and provide other benefits.

Medical marijuana can be used to relieve cancer pain that is resistant to opiate pain killers. Cancer pain has several causes, including inflammation, nerve injury, and tumor growth invading bone and other sensitive tissue. It is chronic and persistent. Cannabinoids act on the body in a different way from opiates, reducing inflammation and stimulating the body to produce a natural analgesic. Medical marijuana does not have the negative side effects of opiate use, such as constipation and confusion. The body does not develop tolerance as it does to opiate drugs, requiring stronger and stronger doses to achieve the same level of comfort.

There is increasing evidence that for some types of cancer cells, medical marijuana triggers apoptosis, the process by which cells kill themselves and are naturally cleaned up by the body. Cancer cells with cannabinoid (CB)1 or CB2 receptors react to the presence of THC or CBD, the two most active ingredients in medical marijuana.

Studies have indicated that some liver, prostate, lung, pancreatic, oral, and colon cancer cells have CB1 and CB2 receptors. Abnormal immune cells in blood cancers such as leukemia also have CB1 and CB2 receptors. Some breast cancers have receptors for CBD. Numerous studies have found that medical marijuana has the potential to kill cancer cells.