This August 2021 study published in the Journal of Neuropsychiatry & Clinical Neurosciences examined the effectiveness of THC administered together with palmitoylethanolamide (PEA) for treatment-resistant Tourette's Syndrome.
It was a 12-week uncontrolled trial of a combination drug called THX-110 (maximum daily Δ9-THC dose = 10 mg, and a constant 800-mg dose of PEA) in 16 adults with Tourette's syndrome.
The primary outcome was improvement on the Yale Global Tic Severity Scale (YGTSS) total tic score.
"Tic symptoms significantly improved over time with THX-110 treatment. Improvement in tic symptoms was statistically significant within 1 week of starting treatment compared with baseline. THX-110 treatment led to an average improvement in tic symptoms of more than 20%, or a 7-point decrease in the YGTSS score."
The abstract of the published paper is here at the PubMed.gov site.