Putting the Medical into Marijuana: Does Evidence Support Use?
A flowering plant, marijuana has for centuries been produced for its plant fiber, hemp. Because of its strength and endurance, hemp is widely used to make ropes and other fibrous products. Evidence of the existence of marijuana, or Cannabis sativa, can be found in prehistoric archaeological sites in Euro-Asia and Africa.1 The oldest known written description of cannabis use is by the Greek historian Herodotus, who wrote more than 400 years BC about Eurasian Scythians using cannabis in steam baths.1,2
Marijuana is the most commonly used illegal drug in the United States.3 Recently, there has been a push for legalization of marijuana because many people now feel that the overall effects of the drug are harmless. Marijuana for recreational use is legal in 4 states, with an additional 19 states approving it for medicinal use.3 Regardless of whether marijuana is legal in individual states, it is still illegal under federal law.
The first and most studied medical use of C sativa is in the control of nausea and vomiting caused by chemotherapy.4 For these patients, the antiemetic action is desirable, and the increased appetite resulting from marijuana use is also beneficial, as most patients need to increase food intake.4 Marijuana is also useful for those with wasting diseases such as acquired immune deficiency syndrome (AIDS).4
The component of C sativa that produces the euphoric feeling is tetrahydrocannabinol (THC).5 The mechanism of action that produces euphoria and relaxation is distributed among several receptors in the central nervous system, collectively recognized as the endocannabinoid system.6 When inhaled, THC is absorbed rapidly into the system, peaking within minutes. Marijuana is known to cross the blood-brain barrier and the placenta, but it is accumulated in fat cells.
Some very small studies have indicated that THC is useful in lowering intraocular pressure in those with glaucoma. Although there have been findings that THC lowers intraocular pressure, the effect is short-term and nonspecific, indicating that low blood pressure and other central nervous system depressive responses also occur.7 In one study, 9 patients with refractory glaucoma were given THC by either smoking or oral tablet.7 At the end of 9 months, all patients had discontinued the study because of the side effects of THC. A rapid tolerance to THC's pressure-reducing action was also noted.
Other areas of potential medical use of THC include the relief of spasticity in neurodegenerative diseases, for pain reduction, and for seizure control, but there have been few trials of adequate design and significance to recommend THC for these conditions. However, there are many anecdotal descriptions of successful treatment with THC in individuals. In 2014, the directors of the Epilepsy Foundation called for much more lenient policies to allow patients to access marijuana in cases where traditional therapy was either not tolerated or ineffective.8