“Preliminary studies suggested that delta-9-tetrahydrocannabinol (THC), the major psychoactive ingredient of Cannabis sativa L., might be effective in the treatment of Tourette syndrome (TS).

This study was performed to investigate for the first time under controlled conditions, over a longer-term treatment period, whether THC is effective and safe in reducing tics in TS.

CONCLUSION:

Our results provide more evidence that THC is effective and safe in the treatment of tics. It, therefore, can be hypothesized that the central cannabinoid receptor system might play a role in TS pathology.”

https://www.ncbi.nlm.nih.gov/pubmed/12716250

“Our results provide more evidence that THC is effective and safe in the treatment of tics.” http://www.psychiatrist.com/jcp/article/Pages/2003/v64n04/v64n0417.aspx