Marijuana (Cannabis sativa) has been a topic of much attention over several decades, initially as a herbal remedy for a variety of ills, then as a mild hallucinogen used by the 'counter culture' of the 1960s and more recently as a focus of increasing medical and scientific research. It also has become a popular alternative medication, and controversy continues to swirl around its indications, despite widespread anecdotal evidence. Cannabinoids, isolated from the plant as well as synthetically derived, have become a rapidly increasing area of research and clinical use in certain medical conditions, such as cancer and cancer treatment. Taken together, it becomes difficult for medical professionals to know whether these compounds can be used with caution or should be rejected outright due to the potential harms, which include the possibility of psychosis and driver impairment. Here, we explore the evidence for cannabis and cannabinoid use in supportive cancer therapy, as well as sift through some of the issues to be considered (including an explanation of the Canadian experience) as 'medical marijuana' becomes more widely available.