Medical Marijuana | Pros, Cons, Debate, Arguments, Health Care, Cannabis, CBD, & THC – Britannica
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The use of medical marijuana dates to ancient civilizations, though historians are undecided about whether the first medical use of cannabis was in China, where the plant is indigenous. [1]
Archaeologists unearthed traces of cannabis with high levels of THC (the main psychoactive component of cannabis) in wooden bowls dating to 500 bce in the Jirzankal Cemetery in China, marking the earliest instance of marijuana use found to date. This particular use of marijuana was more likely for a religious rite than medicinal purposes, though religion and medicine were not necessarily kept separate. Such use was described by Greek historian Herodotus: “The Scythians then take the seed of this hemp and, crawling in under the mats, throw it on the red-hot stones, where it smolders and sends forth such fumes that no Greek vapor-bath could surpass it. The Scythians howl in their joy at the vapor-bath.” [2][3][4]
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The mythological Chinese Emperor Shennong’s pharmacopoeia, Treatise on Medicine (which itself has disputed dates–2737 bce or 1ce and unknown authorship), included marijuana as a treatment for “malaria, constipation, rheumatic pains, ‘absentmindedness’ and ‘female disorders.’” [5][6]
From China, marijuana was introduced to Iran and Anatolia by the Scythians and then spread to India, Greece, Egypt, and throughout Africa. Evidence suggests Arab physicians used marijuana for pain, inflammation, and epileptic seizures, while in India marijuana was used for fevers, sexually transmitted infections (STIs), headaches, sleep, dysentery, digestion, and appetite inducement. In Rome, Emperor Nero’s private physician, Dioscorides, used the plant to treat pain in ears. Marijuana was similarly used in Africa, as evidenced by the Egyptian Ebers papyrus (circa 1550 bce), for fever, pain, infected toenails, and uterine cramps. Other Egyptian papyruses include cannabis as treatment for eye infections (perhaps glaucoma), cholera, menstrual ailments, headaches, schistosomiasis, fever, and colorectal cancer. [1][4][7][8][9][10]
The Moors brought marijuana to Spain during the 8th-century occupation. The Spanish, in turn, took marijuana to the Americas where it was mainly used as a cash crop for producing hemp fiber. Medical use followed quickly, with Mexicans using the drug for gonorrhea, menstrual ailments, pain, and toothaches. [10][11][12][13]
Robert Burton’s The Anatomy of Melancholy (1621) heralded the arrival of marijuana in medieval Europe by suggesting that cannabis be used to treat depression. Thereafter marijuana was recommended for inflammation (New English Dispensatory, 1764) and coughs, STIs, and incontinence (Edinburgh New Dispensary, 1794). [1]
Medical use of marijuana did not gain much popularity in the United Kingdom until W.B. O’Shaughnessy, an Irish professor at the Medical College of Calcutta, India, tested the indigenous Cannabis indica on animals and children after seeing how Indians used marijuana in medicine. O’Shaughnessy reported in 1839 that cannabis was safe and used marijuana to treat rabies, cholera, delirium from alcohol withdrawal, pain, rheumatism, epilepsy, tetanus, and as a muscle relaxer. He deemed marijuana “an anticonvulsant remedy of the greatest value” and brought the drug with him when he returned to England in 1842. [1][7]
The Provincial Medical and Surgical Journal (now the British Medical Journal) put medical cannabis on the front page in 1843, prompting popularity and regular use of the drug as a painkiller, with even Queen Victoria reportedly being prescribed marijuana postpartum and for premenstrual syndrome (PMS) by her private physician J.R. Reynolds. A tincture of marijuana, frequently added to tea, was used commonly in Victorian England. The 1894 Indian Hemp Drugs Commission stated marijuana was not harmful if used in moderation and could be particularly helpful in treating malaria. [7][14]
In 1860, American doctor R.R. M’Meens, crediting W.B. O’Shaughnessy, extolled the virtues of marijuana to treat “tetanus, neuralgia, dysmenorrhea (painful menstruation), convulsions, the pain of rheumatism and childbirth, asthma, postpartum psychosis, gonorrhea, and chronic bronchitis” as well as the drug’s use for sleep-inducement and appetite stimulation. Other American doctors prescribed marijuana for restlessness, anxiety, “senile insomnia,” neuralgia, migraines, depression, gastric ulcers, morphine addiction, and asthma, and as a topical anesthetic. [1]
However, the arrival of marijuana wasn’t lauded by everyone. Mark Stewart, a member of the UK Parliament, complained in 1891 that “the lunatic asylums of India are filled with ganja smokers.” Along with negative associations with mental illness, marijuana was also attacked with racist political commentary. In the United States, the Federal Bureau of Narcotics (FBN) Commissioner Harry Anslinger claimed there were “100,000 total marijuana smokers in the U.S., and most are Negroes, Hispanics, Filipinos and entertainers. Their Satanic music, jazz and swing result from marijuana use. This marijuana causes white women to seek sexual relations with Negroes, entertainers and any others.” Additionally, the agency was concerned that “marihuana leads to pacifism and communist brainwashing.” His efforts were aided by a 1936 anti-marijuana propaganda film, Reefer Madness, as well as by newspaper publisher William Randolph Hearst, who famously printed articles designed to foster fear of the drug. [1][7][13][15] [16]
By the 1890s, marijuana was falling out of favor among doctors, and U.S. states were working to ban marijuana because of the drug’s association with Mexican immigrants. Massachusetts led the charge, passing a ban on the drug in 1911. [7][10]
The FBN, which would merge with other departments to form what is now the Drug Enforcement Administration (DEA), worked to pass the Marihuana Tax Act of 1937. While the law only taxed marijuana, it effectively banned the drug as well as industrial hemp. The Marihuana Tax Act survived until 1969 when it was declared unconstitutional. However, President Richard Nixon would reinstate the marijuana ban in 1970 with the Controlled Substances Act, which classified cannabis as a Schedule 1 drug (“drugs with no currently accepted medical use and a high potential for abuse”), beginning Nixon’s “War on Drugs” and effectively ending medical research on the drug. [7][10][16][37]
In the United Kingdom, the Misuse of Drugs Act was passed in 1971, declaring marijuana to have “no known or limited medical use.” The law now classifies marijuana as a Class B drug, which are considered less dangerous than Class A drugs including cocaine, ecstasy, and crystal meth. Class B drugs include amphetamines, barbiturates, and ketamine, along with marijuana. The possession of any Class B drug carries a penalty of up to 5 years in prison. [7][17] [18]
While the American federal war on drugs would continue, U.S. states began legalizing medical marijuana in the 1990s. California was the first to legalize cannabis for medical use in 1996, quickly followed by Alaska, Oregon, and Washington state in 1998, and Maine in 1999. By July 2025, 39 states and D.C. had legalized medical marijuana, leaving only 11 states where medical marijuana is illegal: Georgia, Idaho, Indiana, Iowa, Kansas, North Carolina, South Carolina, Tennessee, Texas, Wisconsin, and Wyoming. [19]
While states were legalizing medical marijuana, some of the earliest adopting states also began legalizing recreational, or adult-use, marijuana. Colorado and Washington legalized this in 2012—22 other states and D.C. had done so by July 2025. Only states with legal medical marijuana have thus far legalized adult-use marijuana. [20]
On December 18, 2025, President Donald Trump signed “Increasing Medical Marijuana and Cannabidiol Research,” which requires that the “the Attorney General shall take all necessary steps to complete the rulemaking process related to rescheduling marijuana to Schedule III of the CSA in the most expeditious manner in accordance with Federal law.” The order does not legalize or decriminalize marijuana. [52]
Medical marijuana is most commonly used for pain in the U.S. “While marijuana isn’t strong enough for severe pain (for example, post-surgical pain or a broken bone), it is quite effective for the chronic pain that plagues millions of Americans, especially as they age,” explains primary care physician and cannabis specialist, Peter Grinspoon. [22]
Marijuana also offers pain relief for patients who are suffering the pain of multiple sclerosis or general nerve pain. In contrast with marijuana, the commonly prescribed drugs for these ailments are often heavily sedating, which can impair quality of life. [22]
Marijuana, particularly CBD (the main nonpsychoactive component in cannabis), has also shown potential to treat high blood pressure, inflammation and related neuropathic pain, anxiety disorders (including generalized anxiety, panic, social anxiety, obsessive-compulsive, and post-traumatic stress disorders), gastrointestinal (GI) disorders (including irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), Crohn’s, and ulcerative colitis), epilepsy and other seizure syndromes, as well as the prevention of drug and alcohol addiction relapse and alleviation of the effects of chemotherapy. [23][24][25][26][27][28][29][30]
“Medical marijuana” also includes drugs chemically derived from marijuana, rather than only preparations of the plant itself. According to the National Institutes of Health, “THC itself has proven medical benefits in particular formulations.” [31]
In the U.S., the FDA approved THC-based Marinol and Cesamet to treat nausea in chemotherapy patients and for appetite stimulation in AIDS patients. Also FDA-approved is the CBD-based Epidiolex, which treats Dravet and Lennox-Gastaut syndromes in children. Sativex, a THC- and CBD-based drug for multiple sclerosis (MS) patients, is approved for use in the UK, Canada, and some European countries. [31]
The bottom line: marijuana has been used as medicine for thousands of years. The drug should be legalized and studied to reap the full benefits.
Many patients prefer marijuana for pain because it is less addictive and carries less risk of overdose than opiates. [22][32]
Three researchers from the University of British Columbia BC Centre on Substance Use in Vancouver, argue: “Although cannabis use is neither risk free nor a panacea, the risks it poses of physical dependence and accidental overdose compared with opioid use are substantially lower—indeed, fatal overdose with cannabis has never been documented and is thought to be impossible. Especially in the era of the opioid overdose crisis, the common sequelae [results] of opioid use disorder (e.g., fatal overdose, acquisition or transmission of blood-borne diseases) are hardly comparable to those of cannabis use disorder at either individual or population levels. The lower relative risks associated with cannabis are reflected in substantially lower rates of cannabis-associated morbidity, mortality and societal costs compared with opioids in Canada, despite much higher levels of exposure. Simply put: it is not perception that cannabis has fewer relative harms than opioids; it is evidence.” [33]
Marijuana can also be used instead of NSAIDs (Advil and Aleve, for example) if someone has kidney problems, ulcers, or gastroesophageal reflux disease (GERD), making it potentially safer for people with those conditions. [22]
Studies also show many patients prefer to use marijuana instead of lorazepam, clonazepam, and alprazolam for anxiety disorders and instead of sertraline, trazodone, or bupropion for depression. [34]
Widespread American approval of marijuana is seen in the many states that have legalized its use. Since California legalized medical marijuana in 1996, 39 states and D.C. have followed suit as of July 2025. [19]
Additionally, polls and elections for more than 20 years have shown Americans united on the legalization of medical marijuana. Of 96 polls and elections collected by ProCon between 2000 and 2022, only three had less than 50 percent support for legalizing medical marijuana. [35]
Plus, a 2021 study found 70.7 percent of physicians at the 2019 American College of Emergency Physicians’ Annual Conference “believed that cannabis has medical value,” and, further, that 79.6 percent of the physicians would choose marijuana over opioids if cannabis were found to be more effective, and 52.3 percent would choose marijuana if it were found to be equally as effective as opioids. [36]
Approval of legalization crosses party lines as well as age and race demographics in what Pew Research Center deemed “overwhelming support” in an Apr. 16, 2021, poll. Among Democrats, 95 percent believed medical marijuana should be legal, joined by 87 percent of Republicans. [21]
92 percent of white Americans would legalize medical marijuana, along with 91 percent of Black Americans, 89 percent of Asian Americans, and 87 percent of Hispanic Americans. [21]
The largest support among age groups for medical marijuana comes from those aged 18-29 (94 percent) and 65-74 (93 percent). However, no age group dropped below 85 percent approval (those aged 75+). [21]
Medical marijuana enjoys so much support among Americans that many now approve of the legalization of recreational marijuana as well. [21]
Whether medical marijuana is legalized for everyone or only adults, legalization provides everyone more access to the drug. [38]
“An ‘unintended consequence’ of marijuana legalization is the impact on the pediatric population. From prenatal exposure to unintentional childhood exposures, through concerns of adolescence abuse and marijuana use for medicinal indications in children, marijuana exposure can affect pediatric patients at every stage in childhood. Regardless of the stage or reason of exposure, concerns exist about short-term and long-term consequences in a child’s physical and mental health,” argues Sam Wang, Associate Professor of Pediatrics-Emergency Medicine at the University of Colorado School of Medicine. [39]
Adult use of marijuana, medical or otherwise, during pregnancy can cause child development problems during and after pregnancy. If exposed to marijuana before birth, children may be more susceptible to “increased hyperactivity, impulsivity, and inattention symptoms” and problems with “visual-motor coordination, processing speed, [and] visual memory.” [31][39][40][41]
Any drug at home poses potential risks for children, but medical marijuana edibles look like regular treats (gummy bears, hard candies, and chocolate bars, to name a few), yet are infused with potent marijuana. And, unlike a regular treat, a marijuana infused edibles should be carefully portioned for the correct dosage. A child accidentally eating an entire marijuana candy bar could overdose and end up in serious medical distress. Within just five years, accidental cannabis exposures in kids aged one to six who ate edibles increased 1,375 percent from 207 cases in 2017 to 3,054 in 2021. [39][42][47]
The danger does not decrease as children age. According to the National Institutes of Health, “heavy chronic marijuana consumption in young people under the age of 25 has been associated with decreased cognitive and executive function.” Researchers are not yet certain whether the damage is permanent, but one New Zealand study found teens who smoked marijuana heavily and developed a marijuana use disorder lost 8 IQ points on average between ages 13 and 38. [40]
The National Institutes of Health offers a litany of negative mental side effects, including “altered senses (for example, seeing brighter colors), altered sense of time, changes in mood, impaired body movement, difficulty with thinking and problem-solving, impaired memory, hallucinations (when taken in high doses), delusions (when taken in high doses), [and] psychosis (risk is highest with regular use of high potency marijuana).” [40]
Physical side effects include breathing problems such as “daily cough and phlegm, more frequent lung illness, and a higher risk of lung infections,” an increased heart rate (which, in turn, increases the risk of heart attack), and Cannabinoid Hyperemesis Syndrome (“regular cycles of severe nausea, vomiting, and dehydration, sometimes requiring emergency medical attention”). [40]
Further, between 9 percent and 30 percent of people who use marijuana are at risk of developing a substance use disorder. And, with THC levels steadily increasing, the potential for addiction only grows as users need more and more marijuana to feel the desired effects. [40][43]
Colorado legalized medical marijuana in 2000 and recreational marijuana in 2012. The state saw a 40 percent increase in cannabis-related emergency room (ER) visits between 2012 and 2014. Colorado hospitals have seen a 50 percent increase in marijuana-related cyclic vomiting syndrome. Burn admissions also increased. [44]
However, these are the known side effects. Because the drug has not been studied as thoroughly as other drugs, there may be unexpected consequences to medical marijuana use. [44]
A 2025 study of brain function found that 63 percent of heavy lifetime cannabis users and 68 percent of recent cannabis users had reduced brain activity during a working memory task. The study’s authors suspect that the negative effects of cannabis use could be long lasting. [48][49]
Marijuana derivatives may provide some therapeutic benefit for certain individuals in specific circumstances—helping patients control pain, suppress nausea, and improve appetite—but the harms from cannabis are real, they must be recognized and mitigated, and we must not allow a marijuana free-for-all under the guise of medicine. So argues cardiologist Sarah C. Hull.[38]
In fact, a tax on the recreational use of marijuana, decriminalized for adults, could underwrite the additional research needed when it comes to the medical use of marijuana. “There is substantial need for more research to guide specific policy development going forward,” notes Dr. Hull, “and in the meantime, recreational use (though not medicinal use) should be generously taxed to fund research efforts as well as addiction treatment in order to enhance benefits to society.”[38][46]
Moreover, the recent long-term studies that have been completed are alarming. The 2025 meta-study of 15 years of cannabis research revealed that “evidence from randomized clinical trials does not support the use of cannabis or cannabinoids for most conditions for which it is promoted, such as acute pain and insomnia.” More disturbing, the study found that nearly one-third of users of cannabis for medical purposes now had “cannabis use disorder,” characterized by mood swings and memory and learning issues, an inability to control the quantity of marijuana used, problems with fulfilling responsibilities (at work, school or home), a deterioration of one’s physical appearance and social relationships, and hostility to anyone questioning their use of the drug. Chronic users of marijuana also show an increased risk for coronary and cardiovascular diseases, including heart attacks and strokes. (Other studies have raised similar troubling issues.) [50][51]
Clearly, there is ample concern whether the benefits of medical marijuana use outweigh the risks associated with the drug.
Adds cognitive neuroscientist Earl Miller, “Once we understand on the brain level what effect [marijuana] is having on cognition, then we can see how it can be applied for all sorts of purposes, but first we need to know exactly what it’s doing. If it’s going to be introduced to society in a big way, we need to know what the potential harms and benefits are.”[44]
*Please consult the state for the most recent information.*
Why are some states not on this list? Our list includes states that have legalized use of the marijuana plant for medical purposes. States that limit use to the nonpsychoactive marijuana extract called cannabidiol (CBD) are not included on this list. Also not included are states whose legalization laws require physicians to “prescribe” marijuana (an illegal act under federal law) vs. “recommend” marijuana (considered protected free speech between doctor and patient), as well as states that have passed “affirmative defense” laws in which arrested marijuana users are allowed to mention medical use in their defense.
From the 1970s to the 1990s, several states passed symbolic laws that liberalized their medical marijuana policies to some degree. For example, some states wrote laws that legalized medical marijuana with a physician’s prescription, however, those laws are considered symbolic laws because federal law prohibits physicians from “prescribing” marijuana, a schedule I drug. Some states wrote laws creating research programs to investigate medical use of marijuana; others allowed for “medical necessity” as a defense in state court. None of these laws made marijuana available to patients with a doctor’s recommendation, and are thus considered symbolic.
All states require proof of residency to apply to be qualifying patients, although the length of time considered to be a resident varies by state. Some states require registration and registry fees.