The First Long-Term Trial: THC Reduced Tourette Tics Over 6 Weeks | Research

The takeaway

The first controlled long-term trial found that THC (up to 10 mg/day) significantly reduced tics in Tourette syndrome over 6 weeks, with no serious adverse effects, providing the strongest evidence yet for cannabinoid treatment.

Read this if you have Tourette syndrome and want to know about the strongest clinical trial evidence for THC treatment.

Significant tic reduction over 6 weeks (p=0.037) with no serious adverse effects

What the researchers found

In this 6-week randomized, double-blind, placebo-controlled trial, THC (up to 10 mg/day) produced significant improvements or trends toward improvement across multiple tic rating scales. Using patient self-ratings, there was a significant difference between THC and placebo across 10 treatment days. The overall ANOVA also demonstrated a significant difference (p=0.037).

Seven of 24 patients dropped out or were excluded, but only one due to side effects. No serious adverse effects occurred. This was the first controlled trial to demonstrate THC effectiveness for tics over a sustained treatment period rather than a single dose.

Why it matters

This was the landmark trial that moved cannabinoid treatment for Tourette syndrome from promising single-dose studies to evidence of sustained efficacy. The 6-week treatment period with multiple assessment tools and a robust study design provided the strongest evidence to date that THC could be an effective treatment for tics.

The numbers in context

Twenty-four patients enrolled, 17 completed. THC dose up to 10 mg/day. Treatment duration: 6 weeks with 6 assessment visits. Overall ANOVA p=0.037. One dropout due to side effects.

How the study worked

This was a randomized, double-blind, placebo-controlled parallel study. Twenty-four patients with Tourette syndrome (DSM-III-R criteria) were treated for 6 weeks with up to 10 mg/day THC or placebo. Tics were rated at 6 visits using 5 different assessment tools: TS-CGI, STSSS, YGTSS, TSSL (self-rated), and a videotape-based rating scale.

What this study cannot tell us

The sample of 24 patients (17 completers) was still relatively small. The 29% dropout rate, while only partly due to side effects, reduces the interpretability of results. Multiple assessment tools were used, with significance reached on some but not all scales, which could raise concerns about multiple comparisons.

How to read the evidence

This is a randomized, double-blind, placebo-controlled trial over 6 weeks with 24 patients, providing strong evidence as the first sustained-treatment RCT for this indication.

When this study was published

Published in 2003. This remains one of the most cited clinical trials for cannabinoids in Tourette syndrome.

The bigger picture

This trial, combined with the earlier single-dose studies by the same group, established a body of randomized controlled evidence for THC in Tourette syndrome. Although larger trials have not been widely conducted, THC is now used off-label for Tourette syndrome in some clinical settings, and cannabis-based treatments continue to be investigated for this condition.

Questions still open

Why have larger confirmatory trials not been conducted despite these positive results? Would higher THC doses or combined THC/CBD formulations show stronger effects? How does THC compare to conventional Tourette medications in head-to-head trials?

Common questions

How effective is THC for Tourette syndrome tics?

This 6-week trial found statistically significant tic reduction with THC compared to placebo across multiple rating scales. While the effect was not dramatic, it was consistent and achieved with good tolerability, making THC a reasonable option for patients who have not responded to conventional treatments.

Are there long-term side effects of using THC for Tourette syndrome?

This 6-week trial found no serious adverse effects, and only one patient dropped out due to side effects. However, longer-term safety data from controlled trials are limited.

Read the original research

Delta 9-tetrahydrocannabinol (THC) is effective in the treatment of tics in Tourette syndrome: a 6-week randomized trial.

The Journal of clinical psychiatry, 64(4), 459-65

View on PubMed ↗

Citation

Müller-Vahl, Kirsten R; Schneider, Udo; Prevedel, Heidrun; Theloe, Karen; Kolbe, Hans; Daldrup, Thomas; Emrich, Hinderk M. (2003). Delta 9-tetrahydrocannabinol (THC) is effective in the treatment of tics in Tourette syndrome: a 6-week randomized trial.. The Journal of clinical psychiatry, 64(4), 459-65.