Treatment studies with cannabinoids in anorexia nervosa: a systematic review

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Abstract
Introduction
Anorexia nervosa (AN) is a psychiatric disorder with a high mortality and unknown etiology, and effective treatment is lacking. For decades, cannabis has been known to cause physical effects on the human body, including increasing appetite, which may be beneficial in the treatment of AN.

Objective
To systematically review the literature for evidence of an effect of cannabinoids on (1) weight gain, and (2) other outcomes, in AN.

Method
A systematic review was done using three databases Embase, PubMed and Psychinfo. The review was registered in PROSPERO with ID number CRD42019141293 and was done according to PRISMA guidelines.

Results
There were 1288 studies identified and after thorough review and exclusion of copies, 4 studies met the inclusion criteria. Three studies used the same AN population and utilized data from one original study, leaving only two original studies. Both of these were Randomized Controlled Trials that explored the effects of delta-9-tetrahydrocannabinol (Δ9-THC) or dronabinol in AN, whereof one study was properly designed and powered and showed a weight increase of an added 1 kg over 4 weeks over placebo.

Discussion and conclusion
There are few studies and the level of evidence is low. The only properly designed, low bias and highly powered study found a weight increasing effect of dronabinol in AN, while the other, using Δ9-THC at a high dose, found no effect and where the dose may have counteracted the weight gaining effects due to adverse events. More research on cannabinoids in anorexia nervosa is warranted, especially its effects on psychopathology.

Level of evidence
Level I, systematic review.