Medical cannabis, or medical marijuana (MMJ), is cannabis and cannabinoids that are prescribed by physicians for their patients. The use of cannabis as medicine has not been rigorously tested due to production and governmental restrictions, resulting in limited clinical research to define the safety and efficacy of using cannabis to treat diseases.Preliminary evidence has indicated that cannabis might reduce nausea and vomiting during chemotherapy and reduce chronic pain and muscle spasms. Regarding non-inhaled cannabis or cannabinoids, a 2021 review found that it provided little relief against chronic pain and sleep disturbance, and caused several transient adverse effects, such as cognitive impairment, nausea, and drowsiness.Short-term use increases the risk of minor and major adverse effects. Common side effects include dizziness, feeling tired, vomiting, and hallucinations. Long-term effects of cannabis are not clear. Concerns include memory and cognition problems, risk of addiction, schizophrenia in young people, and the risk of children taking it by accident.The Cannabis plant has a history of medicinal use dating back thousands of years in many cultures. Some American medical organizations have requested removal of cannabis from the list of Schedule I controlled substances maintained by the United States federal government, followed by regulatory and scientific review. Others oppose its legalization, such as the American Academy of Pediatrics.Medical cannabis can be administered through various methods, including capsules, lozenges, tinctures, dermal patches, oral or dermal sprays, cannabis edibles, and vaporizing or smoking dried buds. Synthetic cannabinoids are available for prescription use in some countries, such as dronabinol and nabilone. Countries that allow the medical use of whole-plant cannabis include Argentina, Australia, Canada, Chile, Colombia, Germany, Greece, Israel, Italy, the Netherlands, Peru, Poland, Portugal, Spain, and Uruguay. In the United States, 37 states and the District of Columbia have legalized cannabis for medical purposes, beginning with the passage of California's Proposition 215 in 1996. Although cannabis remains prohibited for any use at the federal level, the Rohrabacher–Farr amendment was enacted in December 2014, limiting the ability of federal law to be enforced in states where medical cannabis has been legalized.