Medical cannabis, medicinal cannabis or medical marijuana (MMJ) includes cannabis products and cannabinoid molecules that are prescribed by physicians for their patients. The use of cannabis as medicine has a long history, but has not been as rigorously tested as other medicinal plants due to legal and governmental restrictions, resulting in limited research to define the safety and efficacy of using cannabis to treat diseases.
There is mixed and inconclusive evidence on the benefits of cannabis-based medicines, frequent mild adverse effects, and generally low-to-moderate quality of evidence. Cannabis-based medicines may offer modest relief for chronic, especially neuropathic, pain and slight improvements in function and sleep in chronic pain patients, but evidence is limited and inconsistent; mild harms may outweigh the benefit and placebo effects may influence trial outcomes. Recent clinical reviews have concluded that evidence remains insufficient to support the use of cannabis or cannabinoids for most medical indications, emphasizing that modest potential benefits must be weighed against established risks.
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.
Many cultures have used cannabis for therapeutic purposes for thousands of years. Some American medical organizations have requested removal of cannabis from the list of Schedule I controlled substances, emphasizing that rescheduling would enable more extensive research and regulatory oversight to ensure safe access. Others oppose its legalization, such as the American Academy of Pediatrics. 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, 38 states and the District of Columbia have legalized cannabis for medical purposes, beginning with the passage of California's Proposition 215 in 1996.
Classification
In the U.S., the National Institute on Drug Abuse defines medical cannabis as "using the whole, unprocessed marijuana plant or its basic extracts to treat symptoms of illness and other conditions".
A cannabis plant includes more than 400 different chemicals, of which about 70 are cannabinoids. In comparison, typical government-approved medications contain only one or two chemicals. The number of active chemicals in cannabis is one reason why treatment with cannabis is difficult to classify and study.
A 2014 review stated that the variations in ratio of CBD-to-THC in botanical and pharmaceutical preparations determines the therapeutic vs psychoactive effects (CBD attenuates THC's psychoactive effects) of cannabis products.
Medical uses and research
A scoping review of 72 systematic reviews found mixed and inconclusive evidence on the benefits of cannabis-based medicines, frequent mild adverse effects, and generally low-to-moderate quality of evidence.
Low quality evidence suggests its use for reducing nausea during chemotherapy, improving appetite in HIV/AIDS, improving sleep, and improving tics in Tourette syndrome. When usual treatments are ineffective, cannabinoids have also been recommended for anorexia, arthritis, glaucoma.
It is unclear whether American states might be able to mitigate the adverse effects of the opioid epidemic by prescribing medical cannabis as an alternative pain management drug.
Cannabis should not be used in pregnancy.
Pain Cannabis-based medicines may provide modest relief for chronic pain, particularly neuropathic pain, as well as small improvements in physical function and sleep in chronic pain patients. Cannabis-based medicines show limited and inconsistent evidence for pain relief, with mild harms commonly reported that may outweigh potential benefits.
Short-term use of oral or sublingual cannabis, particularly high-THC synthetic or comparable-THC extracted products, may modestly reduce chronic pain but increases risks of dizziness, sedation, and other adverse effects, with limited evidence on long-term outcomes.
Placebo effects contribute to pain reduction in cannabinoid clinical trials, and while media attention is high, it does not directly correlate with clinical outcomes but may influence future expectations and trial results.
Insomnia Cannabis administration does not have a noted effect on sleep. Cannabis withdrawal is associated with a reduction in hours spent asleep, an increase in the duration of sleep onset, and rapid eye movement rebounds.
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 (CHS).
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, lightheadedness and dry mouth".
HIV/AIDS 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.
Neurological conditions Cannabis' efficacy is not clear in treating neurological problems, including multiple sclerosis (MS) and movement problems. Evidence also suggests that oral cannabis extract is effective for reducing patient-centered 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, cannabidiol, 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.
Mental health
Evidence for cannabis and cannabinoids in mental health treatment is limited and low-quality; they show no benefit for most mental disorders, increase general adverse events, and are not justified for routine use. Risks (including cannabis-induced psychotic disorder, worsening bipolar symptoms, and cannabis use disorder) are substantial, especially in vulnerable populations.
The relationship between cannabis use and anxiety symptoms is complex, and while some users report relief, the overall evidence from observational studies and clinical trials remains inconclusive.
Cannabis use, especially at high doses, is associated with a higher risk of psychosis, particularly in individuals with a genetic predisposition to psychotic disorders like schizophrenia. Some studies have shown that cannabis can trigger a temporary psychotic episode, which may increase the risk of developing a psychotic disorder later.
The impact of cannabis on depression is less clear. Some studies suggest a potential increase in depression risk among adolescents who use cannabis, though findings are inconsistent across studies.
Adverse effects
Medical use There is insufficient data to draw strong conclusions about the safety of medical cannabis. Typically, adverse effects of medical cannabis use are not serious; they include tiredness, dizziness, increased appetite, and cardiovascular and psychoactive effects. Other effects can include impaired short-term memory; impaired motor coordination; altered judgment; and paranoia or psychosis at high doses. Tolerance to these effects develops over a period of days or weeks. The amount of cannabis normally used for medicinal purposes is not believed to cause any permanent cognitive impairment in adults, though long-term treatment in adolescents should be weighed carefully as they are more susceptible to these impairments. Withdrawal symptoms are rarely a problem with controlled medical administration of cannabinoids. The ability to drive vehicles or to operate machinery may be impaired until a tolerance is developed. Although supporters of medical cannabis say that it is safe, further research is required to assess the long-term safety of its use.
Cognitive effects
Recreational use of cannabis is associated with cognitive deficits, especially for those who begin to use cannabis in adolescence. there is a lack of research into long-term cognitive effects of medical use of cannabis, but one 12-month observational study reported that "MC patients demonstrated significant improvements on measures of executive function and clinical state over the course of 12 months".
Impact on psychosis
Exposure to THC can cause cannabis-induced psychotic disorder (CIPD) in healthy individuals and people susceptible to schizophrenia.
A 2007 meta analysis concluded that cannabis use reduced the average age of onset of psychosis by 2.7 years relative to non-cannabis use. A 2005 meta analysis concluded that adolescent use of cannabis increases the risk of psychosis, and that the risk is dose-related. A 2004 literature review on the subject concluded that cannabis use is associated with a two-fold increase in the risk of psychosis, but that cannabis use is "neither necessary nor sufficient" to cause psychosis. A French review from 2009 came to a conclusion that cannabis use, particularly that before age 15, was a factor in the development of schizophrenic disorders. A 2026 meta-analysis linked cannabis use to an earlier age of psychosis onset.
Pharmacology The genus Cannabis contains two species which produce useful amounts of psychoactive cannabinoids: Cannabis indica and Cannabis sativa, which are listed as Schedule I medicinal plants in the US; a third species, Cannabis ruderalis, has few psychogenic properties. Cannabis contains more than 460 compounds; at least 80 of these are cannabinoids – chemical compounds that interact with cannabinoid receptors in the brain. As of 2012, more than 20 cannabinoids were being studied by the U.S. FDA.
The most psychoactive cannabinoid found in the cannabis plant is tetrahydrocannabinol (or delta-9-tetrahydrocannabinol, commonly known as THC). Other cannabinoids include delta-8-tetrahydrocannabinol, cannabidiol (CBD), cannabinol (CBN), cannabicyclol (CBL), cannabichromene (CBC) and cannabigerol (CBG); they have less psychotropic effects than THC, but may play a role in the overall effect of cannabis. The most studied are THC, CBD and CBN.
CB1 and CB2 are the primary cannabinoid receptors responsible for several of the effects of cannabinoids, although other receptors may play a role as well. Both belong to a group of receptors called G protein-coupled receptors (GPCRs). CB1 receptors are found in very high levels in the brain and are thought to be responsible for psychoactive effects. CB2 receptors are found peripherally throughout the body and are thought to modulate pain and inflammation.
Absorption Cannabinoid absorption is dependent on its route of administration.