Cannabis, also known as marijuana, is a plant from Central Asia but is grown in several parts of the world today. This plant produces cannabinoids – active chemical compounds that cause drug-like effects all over the body, including the central nervous system and the immune system. The best-known psychoactive cannabinoids in Cannabis are delta-9-tetrahydrocannabinol (delta-9-THC) and cannabidiol (CBD). Even though Cannabis is known as the most commonly abused illegal drug, several studies have shown its medicinal benefits for a growing number of diseases and disorders. Besides its anti-inflammatory activity, antiviral activity and relieving muscle spasms caused by multiple sclerosis, Cannabis and cannabinoids have especially high potential in treating cancer and symptoms related to cancer treatment (1, 2, 3, 4).
Preclinical laboratory and animal studies on mice and rats have shown that cannabinoids may inhibit tumor growth by causing cell death, blocking cell growth, and blocking the development of blood vessels needed by tumors to grow. They may even lessen the number and spread of tumors. Besides, they may also kill cancer cells while having only little effect on normal cells or even protect normal cells (1, 3, 4). Studies with CBD showed that this compound given along with chemotherapy may make chemotherapy more effective and increase cancer cell death without harming normal cells (1). Many animal studies have also shown that delta-9-THC and other cannabinoids stimulate appetite, reduce anxiety and prevent vomiting and nerve problems (pain, numbness, tingling, swelling, and muscle weakness) caused by certain types of chemotherapy (1, 3).
Even though no clinical trial (research study with people) on Cannabis as a treatment for cancer in humans exist in the complementary and alternative medicine (CAM) subset of PubMed, various clinical trials where Cannabis and cannabinoids have been studied for ways to manage side effects of cancer therapies have been conducted. 
For example, chemotherapy-related nausea and vomiting can be treated by two cannabinoid drugs, dronabinol and nabilon (that contain delta-9-THC) which were already approved by the Food and Drug Administration (FDA) (1, 2, 4). Clinical trials showed that they work as well as or better than some of the weaker FDA-approved drugs to relieve nausea and vomiting (1). Several studies have also shown that Cannabis relives pain. For example, vaporized Cannabis in combination with morphine relieved pain better than morphine alone. An observational study of nabilone relieved cancer pain along with nausea, anxiety, and distress when compared with no treatment. However, neither dronabinol nor nabilone is approved by the FDA for pain management. Clinical trials also showed improved mood, improved sense of well-being, and less anxiety when inhaling Cannabis, while there are no published studies of the effect of inhaled Cannabis on cancer patients with loss of appetite (1).
Although all these studies look very promising, there is not enough evidence yet to recommend to patients that they should inhale or ingest Cannabis as a treatment for cancer-related symptoms or side effects of cancer therapy. Except of dronabinol and nabilone treatment of chemotherapy-related nausea and vomiting, Cannabis is not approved by the U.S. FDA for the treatment of any cancer-related symptom or side effect of cancer therapy. With more evidence this might change in the future as well.
By Katarina Kovac, PhD, BioSistemika LLC
