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 suggests that cannabis can reduce nausea and vomiting during chemotherapy, improve appetite in people with HIV/AIDS, reduces chronic pain and muscle spasms and treats severe forms of epilepsy.
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 Australia, Canada, Chile, Colombia, Germany, Greece, Israel, Italy, the Netherlands, Peru, Poland, Portugal, and Uruguay. In the United States, 33 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.
Nausea and vomiting
Medical cannabis is somewhat effective in chemotherapy-induced nausea and vomiting (CINV) and may be a reasonable option in those who do not improve following preferential treatment. Comparative studies have found cannabinoids to be more effective than some conventional antiemetics such as prochlorperazine, promethazine, and metoclopramide in controlling CINV, but these are used less frequently because of side effects including dizziness, dysphoria, and hallucinations. Long-term cannabis use may cause nausea and vomiting, a condition known as cannabinoid hyperemesis syndrome.
A 2016 Cochrane review said that cannabinoids were "probably effective" in treating chemotherapy-induced nausea in children, but with a high side-effect profile (mainly drowsiness, dizziness, altered moods, and increased appetite). Less common side effects were "ocular problems, orthostatic hypotension, muscle twitching, pruritus, vagueness, hallucinations, light-headedness and dry mouth".
Evidence is lacking for both efficacy and safety of cannabis and cannabinoids in treating patients with HIV/AIDS or for anorexia associated with AIDS. As of 2013, current studies suffer from the effects of bias, small sample size, and lack of long-term data.
A 2017 review found only limited evidence for the effectiveness of cannabis in relieving chronic pain in several conditions. Another review found tentative evidence for use of cannabis in treating peripheral neuropathy, but little evidence of benefit for other types of long term pain.
When cannabis is inhaled to relieve pain, blood levels of cannabinoids rise faster than when oral products are used, peaking within three minutes and attaining an analgesic effect in seven minutes. A 2014 review found limited and weak evidence that smoked cannabis was effective for chronic non-cancer pain. A 2015 meta-analysis found that inhaled medical cannabis was effective in reducing neuropathic pain in the short term for one in five to six patients. Another 2015 review found limited evidence that medical cannabis was effective for neuropathic pain when combined with traditional analgesics.
A 2011 review considered cannabis to be generally safe, and it appears safer than opiods in palliative care
Cannabis' efficacy is not clear in treating neurological problems, including multiple sclerosis (MS) and movement problems. The combination of Δ9-tetrahydrocannabinol (THC) and cannabidoil (CBD) extracts give subjective relief of spasticity, though objective post-treatment assessments do not reveal significant changes. Evidence also suggests that oral cannabis extract is effective for reducing patient-centred measures of spasticity. A trial of cannabis is deemed to be a reasonable option if other treatments have not been effective. Its use for MS is approved in ten countries. A 2012 review found no problems with tolerance, abuse, or addiction. In the United States, cannabidoil, one of the cannabinoids found in the marijuana plant, has been approved for treating two severe forms of epilepsy, Lennox-Gastaut syndrome and Dravet syndrome.
Posttraumatic stress disorder
There is no good evidence that medical cannabis is effective for treating posttraumatic stress disorder, and its use for this purpose is not recommended.