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A woman's debilitating chronic itch disappeared after she started using marijuana

close-up of woman's hand scratching an itch on her arm
(Image credit: Shutterstock)

A woman's chronic itch defied all types of treatment, from steroids to opioids to light therapy, but it finally dissipated after her doctors told her to try cannabis.

The woman had dealt with chronic itch symptoms — medically known as chronic pruritus — for a decade, according to a report published April 9 in the Journal of the American Medical Association (JAMA) Dermatology.

Chronic pruritus specifically refers to itching that persists for more than six weeks, and the symptom can be associated with a variety of diseases, including eczema, hyperthyroidism and certain nerve disorders, according to a 2013 report in the New England Journal of Medicine (NEJM). In the woman's case, her pruritus derived from a disease of the bile ducts of the liver called primary sclerosing cholangitis

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There are several theories as to how this disease leads to itchiness but generally, the condition disrupts the normal production of bile, which can lead to a buildup of irritating chemicals under the skin, according to "Itch: Mechanisms and Treatment" (CRC Press/Taylor & Francis, 2014). 

Due to her bile duct condition, the woman also developed lichen amyloidosis, in which raised, dark, itchy bumps appear on the skin and sometimes meld together into thick plaques. The woman had these plaques on her trunk and limbs, accompanied by "extreme" itchiness. 

The woman's primary sclerosing cholangitis was kept under control with medicine and remained stable through time, but her itchiness did not improve. Doctors had previously prescribed a laundry list of treatments to combat this pervasive itching, including topical and oral corticosteroids; an opioid nasal spray; naltrexone, which works against the effects of opioids; and phototherapy, which involves exposing the affected skin to ultraviolet light. 

When all these treatments proved unsuccessful, her doctors turned to medical cannabis. Previous studies have hinted that topical and synthetic cannabinoid treatments can provide at least some relief from itchiness, they noted in the JAMA report. In addition, laboratory studies in animals and cells have hinted at possible explanations as to how the drugs dial down itchy sensations, according to a 2020 review in Journal of the American Academy of Dermatology 

They recommended she use cannabis two nights a week, either by smoking medical marijuana with 18% tetrahydrocannabinol (THC), the main psychoactive ingredient in cannabis, or by taking cannabis in tincture form by placing a liquid extract under her tongue.

"Within 10 minutes after the initial administration, her Worst Itch Numeric Rating Scale (WI-NRS) score improved from 10 of 10 to 4 of 10," her doctors wrote in the JAMA report. This scale ranges from 0 ("no itch") to 10 ("worst imaginable itch"). 

The doctors followed up with the woman after five months of treatment and then again after a full year, and they found that she consistently rated her average daily itchiness as 4 out of 10, a drastic improvement from her previous 10 out of 10. At the 16-month and 20-month follow-ups, her itchiness rating plummeted even lower, falling to 0 out of 10.

"Aside from mild sedation, she reported no adverse effects," her doctors wrote. In addition, "she reported an improvement in quality of life," based on a scoring system called the Dermatology Life Quality Index. She was also able to stop taking her other prescribed medications.

The exact mechanism by which cannabis reduced the woman's itching is unknown, but her doctors presented several theories. 

For instance, THC binds to various receptors in the endocannabinoid system, increasing the activity of some while decreasing that of others. The activation of CB1 receptors in the spinal cord and brain, and of both CB1 and CB2 receptors in nerves elsewhere in the body, has been associated with increased pain thresholds, lower nerve cell activation and decreased inflammation, they wrote. In addition, a receptor called TRPV1 helps trigger our sensation of itch, and cannabinoids lock this receptor into a "closed" position, effectively blocking its itch signals.

While this particular patient benefited from the use of cannabis with minimal side effects, the risks and benefits of the treatment still need to be assessed on a larger scale, "especially in its various routes of administration," the doctors wrote. Cannabinoid use has been linked to cognitive impairment, loss of motor coordination, and when smoked, chronic bronchitis symptoms, they wrote in the study.

So while the results of the woman's case are "promising … randomized clinical trials are needed to confirm the results," the doctors wrote. Other researchers have called for such trials in the past, in order to evaluate the benefits of cannabis for chronic itch and to standardize dosing and the course of treatment, according to the Journal of the American Academy of Dermatology report.

Originally published on Live Science.