Double-blind study on THC + CBD and severe Tourette Syndrome

This was a randomized double-blind, crossover trial of the effectiveness of THC + CBD oil on patients with severe Tourette Syndrome. It was published in the New England Journal of Medicine's publication Evidence in June 2023.

The study's structure:

  • participants chosen had a severe burden of tics, moderate levels of obsessive-compulsive disorder and anxiety, and mild levels of depression. 
  • 22 total patients were randomly assigned to a 6-week treatment period with escalating doses of an oral oil containing 5 mg/ml of THC and 5 mg/ml of CBD followed by a 6-week course of placebo, or vice versa, separated by a 4-week washout period.
  • They used the Yale Global Tic Severity Scale, or YGTSS (a clinician-rated instrument considered as the gold standard for assessing tics in patients with Tourette's Syndrome and other tic disorders)
  • They all used the same product. It was an oral formulation with 5 mg/ml of THC and 5 mg/ml of CBD (both plant-derived) in medium-chain triglyceride (MCT) oil.

Dosages started at 1 ml per day (5 mg of THC and 5 mg of CBD) and increased by 1 ml every 7 days up to a maximum of 4 ml daily (20 mg of THC and 20 mg of CBD). Several patients only increased their daily dose to 3 ml/day.

One interesting measurement showed that the cannabinoid metabolites in the patients' blood varied significantly. One patient who took only 0.25 ml/day showed higher blood plasma concentrations of 11-COOH-THC (a D9-THC metabolite) than several patients who took the maximum 4 ml/day dose. This reinforces many other studies that show human metabolism and bioavailability of cannabinoids can vary considerably. We all have unique biochemistry and sometimes even unique liver enzymes.

The authors' observed:

a greater decrease (improvement) in tic score over time with active treatment

In severe Tourette syndrome, treatment with THC and CBD reduced tics and may reduce impairment due to tics, anxiety, and obsessive-compulsive disorder 


There were some mild adverse effects reported during both the placebo period (32% of patients) and active treatment period (36% of patients). The active treatment period reported mostly mild cognitive issues like short term memory loss and poor concentration. 


The full text article is here at NEJM Evidence.