Evidence-Based Reviews

Medical marijuana: Do the benefits outweigh the risks?

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Limited evidence supports its use for treating some conditions, but risks may be substantial.

VIDEO: Dr. Gupta discusses studies evaluating medical marijuana for treating medical and psychiatric disorders.



There is a need for additional treatment options to improve symptoms, enhance the quality of life (QOL), and reduce suffering among patients who have chronic medical illness. Medical marijuana (MM) has the potential to help patients who have certain medical conditions in states where it is legal for prescription by a licensed medical provider.

Cannabis has a long history of medicinal use (Box 11-12). Two derivatives of the Cannabis plant—cannabinoid delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD)—are responsible for most of its effects. Some of these effects, including analgesia, decreased muscle spasticity, and reduced eye pressure, have been harnessed for their potential therapeutic effects (Box 213-19). As of November 2017, 29 states had legalized Cannabis for medical use, and several had legalized its recreational use.12

With the increasing availability of MM, psychiatrists are likely to encounter patients who are using it or who will ask them about it. This article reviews evidence related to using MM to treat patients with neuropathic pain; chemotherapyinduced nausea and vomiting (CINV); epilepsy; multiple sclerosis (MS); glaucoma; Crohn’s disease; Parkinson’s disease; amyotrophic lateral sclerosis; dementia-related behavioral disturbances; posttraumatic stress disorder (PTSD); and anxiety.

Box 1
Cannabis: A history of medicinal use

Cannabis has been cultivated since ancient times, beginning in China and India. The earliest reference of its use for healing purposes may have been in the Chinese Pharmacopeia, circa 1500 BC.1 In 1839, Dr. William Brooke O’Shaughnessy introduced Cannabis Indica, or “Indian hemp,” to the western world after a professorship in Calcutta, India.2 In the early 1840s, an English physician, Dr. John Clendinning, prescribed Cannabis for migraine headache.3 In the 19th and early 20th centuries, several prominent physicians advocated using Cannabis for migraines; Sir William Osler did so in his textbook, The principles and practice of medicine.4 It was listed in the U.S. Pharmacopeia in 1850 but removed in 1942.5,6

Until 1937, Cannabis was used in the United States for medicinal purposes, such as for treating inflamed skin, incontinence, and sexually transmitted diseases.7 In 1937, the Marihuana Tax Act, which prohibited the production, importation, possession, use, and dispersal of Cannabis, was passed.8 Cannabis became a Schedule I drug under the Controlled Substance Act of 1970.9

In 1999, based on available evidence, the Institute of Medicine (IOM) concluded Cannabis had less likelihood of dependence than benzodiazepines, opiates, cocaine, or nicotine. The IOM also concluded that the symptoms of withdrawal were mild in comparison with benzodiazepines or opiates. Finally, the IOM stated that Cannabis was not a “gateway” drug.10

In 1996, California was the first state to reimplement medicinal use of Cannabis under the Compassionate Use Act, also known as Proposition 215.11 This act allowed individuals to retain or produce Cannabis for personal consumption with a physician’s approval. Many states eventually followed California’s lead. As of November 2017, 29 states, the District of Columbia, Guam, and Puerto Rico had regulated Cannabis use for medical purposes,12 and recreational use had been approved in 7 states and the District of Columbia.

Medical illnesses

Neuropathic pain. Chronic neuropathic pain affects an estimated 7% to 8% of adults.20 Patients with neuropathic pain are often treated with anticonvulsants, anti­depressants, opioids, and local anesthetics21; however, these medications may not provide substantial relief. Research has revealed that THC and CBD can improve central and peripheral neuropathic pain, as well as pain associated with rheumatoid arthritis and fibromyalgia.22

Wilsey et al23 evaluated the analgesic effects of smoked MM for neuropathic pain in a small (N = 38) double-blind, randomized controlled trial (RCT). Patients in this study had a preexisting diagnosis of complex regional pain syndrome, spinal cord injury, peripheral neuropathy, or nerve injury. To prevent any unforeseen adverse outcomes related to Cannabis use, participants were required to have previous exposure to Cannabis. Patients were excluded if they had major mental illness, substance abuse, or other major medical ailments.

Participants smoked high-dose Cannabis cigarettes (7% THC), low-dose Cannabis cigarettes (3.5% THC), or placebo cigarettes. Pain was measured on a visual analog scale (VAS) that ranged from 0 (no pain) to 100 (worst possible pain). Compared with the placebo group, significant analgesia was achieved in both Cannabis groups (P = .016). The high-dose group had greater neurocognitive impairment.


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