DEAR MAYO CLINIC: Medical marijuana is now legal in the state where I live. What conditions can it be used for and how effective is it? Do people who use medical marijuana need to be concerned about addiction?
ANSWER: Medical marijuana, also called medical cannabis, can be helpful in treating a variety of conditions. The specific disorders it can legally be used to treat vary from state to state. To date, it appears to be most effective for treating muscle spasms, chronic pain and nausea. The U.S. Food and Drug Administration (FDA) recently approved a form of medical cannabis to treat severe childhood epilepsy. There is no convincing evidence that cannabis used to treat medical conditions leads to cannabis dependence.
Marijuana comes from the Cannabis plant. In its leaves and buds are substances called cannabinoids. The plant contains more than 100 cannabinoids, but two are of particular interest for medical purposes: THC (delta-9 tetrahydrocannabinol) and CBD (cannabidiol). THC is the primary mind-altering ingredient in marijuana that makes people "high." CBD does not trigger changes in the brain that lead to a high.
Possession of marijuana is illegal under federal law in the U.S. However, 30 states and the District of Columbia currently have laws legalizing medical cannabis in some form. To obtain medical cannabis in those states, your health care provider certifies that you have a condition that allows you to buy medical cannabis from an authorized dispensary.
The conditions that qualify for treatment with medical cannabis differ considerably among the states where it's legal. Some states have only a few qualifying conditions, while others have dozens.
A recent report from the National Academies of Science reviewed and summarized the medical literature published about medical cannabis, specifically examining its effectiveness and safety. It concluded that medical cannabis was particularly effective for easing chronic pain, especially pain caused by nerve damage. It can effectively control nausea and vomiting and is often used to manage those symptoms in people undergoing chemotherapy. Medical cannabis also has been shown to be useful in relieving painful muscles spasms caused by conditions such as multiple sclerosis or spinal cord injuries.
The drug approved by the FDA for epilepsy is a liquid medication that's sold under the brand name Epidiolex. It can be used for patients age 2 and older to treat two rare and severe forms of epilepsy: Lennox-Gastaut syndrome and Dravet syndrome. Epidiolex is a pharmacy-grade product composed almost entirely of CBD. It's the first FDA-approved drug that contains a purified drug substance that comes from marijuana.
Examples of additional conditions that may benefit from treatment with medical cannabis, and are approved for its use in some states, include anxiety and depression, amyotrophic lateral sclerosis (ALS), inflammatory bowel disease, Tourette syndrome, post-traumatic stress disorder and autism. Additional study is needed to further define the specific benefits medical cannabis may have for these and other related disorders.
If you are interested in exploring medical cannabis as a treatment option for a disease or condition you have, talk with your health care provider. If your provider isn't familiar with it, ask if there's another clinician in his or her practice who can answer your questions. In states where medical cannabis is legal, the state's department of health often has a website with details and resources to help patients who want to learn more about the benefits and risks of medical cannabis. -- Jon Ebbert, M.D., Community Internal Medicine, Mayo Clinic, Rochester, Minn.