Tourette syndrome (TS) is a complex neuropsychiatric disorder of unknown etiology that is characterized by involuntary vocal tics. Severity of this condition varies widely among patients. Though there is no cure for Tourette syndrome, the condition often improves with age. Experts estimate that 100,000 Americans are afflicted with TS.
A review of the scientific literature reveals several case reports and a small number of clinical trials specific to the use of cannabinoids for the treatment of TS. One of the first appears in the American Journal of Psychiatry in 1999. Investigators at Germany's Medical School of Hanover, Department of Clinical Psychiatry and Psychotherapy, reported successful treatment of Tourette syndrome with a single dose of 10 mg of delta-9-THC in a 25-year-old male patient in an uncontrolled open clinical trial. Investigators reported that the subject's total tic severity score fell from 41 to 7 within two hours following cannabinoid therapy, and that improvement was observed for a total of seven hours. "For the first time, patients' subjective experiences when smoking marijuana were confirmed by using a valid and reliable rating scale," authors concluded.
Investigators confirmed these preliminary results in a randomized, double-blind, placebo-controlled, crossover, single dose trial of THC in 12 adult TS patients. Researchers reported a "significant improvement of tics and obsessive-compulsive behavior (OCB) after treatment with delta-9-THC compared to placebo." Investigators reported no cognitive impairment in subjects following THC administration and concluded, "THC is effective and safe in treating tics and OCB in TS."
Investigators later conducted a second randomized, double-blind, placebo-controlled trial involving 24 patients administered daily doses of up to 10 mg of THC over a six-week period. Researchers reported that subjects experienced a significant reduction in tics following long-term cannabinoid treatment, and suffered no detrimental effects on learning, recall or verbal memory. A trend toward significant improvement of verbal memory span during and after therapy was also observed.
A 2003 review of the data published in the journal Expert Opinions in Pharmacotherapy, reported that in adult TS patients, "Therapy with delta-9-THC should be tried ... if well established drugs either fail to improve tics or cause significant adverse effects." Another scientific review similarly concluded: "[B]y many experts THC is recommended for the treatment of TS in adult patients, when first line treatments failed to improve the tics. In treatment resistant adult patients, therefore, treatment with THC should be taken into consideration."
A 2016 case study reported that the twice daily administration of cannabinoid extracts in a patient with treatment-resistant TS was associated with an 85 percent reduction in the subject's motor tics and a 90 percent reduction in vocal tics. Authors concluded, "Our results support previous research suggesting that cannabinoids are a safe and effective treatment for TS and should be considered in treatment-resistant cases." Another recent pair of case reports acknowledged that the daily administration of cannabis-based therapy "provided significant symptom improvement" in patients with treatment resistant TS.
Most recently, University of Toronto investigators retrospectively assessed the safety and efficacy of inhaled cannabis in 19 patients with TS. Researchers reported, "All study participants experienced clinically significant symptom relief," including reductions in obsessive-compulsive symptoms, impulsivity, anxiety, irritability, and rage outbursts. Eighteen of 19 patients experienced decreased tic severity. Cannabis was "generally well tolerated" by study subjects. They concluded: "Overall, these study participants experienced substantial improvements in their symptoms. This is particularly striking given that almost all participants had failed at least one anti-tic medication trial. ... In conclusion, cannabis seems to be a promising treatment option for tics and associated symptoms."
 Muller-Vahl et al. 1999. Treatment of Tourette's syndrome with delta-9-tetrahydrocannabinol. American Journal of Psychiatry 156: 495.
 Muller-Vahl et al. 2002. Treatment of Tourette's syndrome with Delta-9-tetrahydrocannabinol (THC): a randomized crossover trial. Pharmacopsychiatry 35: 57-61.
 Muller-Vahl et al. 2001. Influence of treatment of Tourette syndrome with delta9-tetrahydrocannabinol (delta9-THC) on neuropsychological performance. Pharmacopsychiatry 34: 19-24.
 Muller-Vahl et al. 2002. op. cit.
 Muller-Vahl et al. 2003. Delta 9-tetrahydrocannabinol (THC) is effective in the treatment of tics in Tourette syndrome: a 6-week randomized trial. Journal of Clinical Psychiatry 64: 459-65.
 Muller-Vahl et al. 2003. Treatment of Tourette syndrome with delta-9-tetrahydrocannabinol (delta 9-THC): no influence on neuropsychological performance. Neuropsychopharmacology 28: 384-8.
 Kirsten Muller-Vahl. 2003. Cannabinoids reduce symptoms of Tourette's syndrome. Expert Opinions in Pharmacotherapy 4: 1717-25.
 Trainor et al. 2016. Severe motor and vocal tics controlled with Sativex. Australasian Psychiatry.
 Jakubovski and Muller-Vahl. 2017. Speechless in Gilles de la Tourette Syndrome: Cannabis-based medicines improve severe vocal blocking tics in two patients. International Journal of Molecular Sciences 18: 1739.
 Abi-Jaoude et al. 2017. Preliminary evidence on cannabis effectiveness and tolerability for adults with Tourette Syndrome. Journal of Neuropsychiatry and Clinical Neuroscience [online ahead of print]