Small Pilot Trial Tests Medicinal Cannabis for Teen Tourette Syndrome, Finds Protocol Feasible but Efficacy Questions Remain

With only 10 participants randomized and seven completing the full protocol, this phase I/II crossover study from Melbourne cannot confirm treatment benefits but establishes that a properly powered, placebo-controlled trial of medicinal cannabis in adolescents with Tourette Syndrome is both feasible and acceptable to families.

Why This Matters

Tourette Syndrome affects roughly 1% of school-age children and adolescents, and the existing pharmacological options carry significant side-effect burdens that many families find unacceptable. Cannabis-based medicines have attracted intense patient and parent interest, yet no registered clinical trials have examined their use specifically in pediatric Tourette populations. Before researchers can ethically and rigorously test whether these products actually reduce tics in teenagers, they first need to demonstrate that such a trial can be safely and reliably conducted. That is the narrow but essential question this study addresses.

Clinical Summary

Tourette Syndrome in adolescence presents a particularly challenging treatment window: tics often peak in severity during a developmental period when tolerability concerns with dopamine-blocking agents and alpha-2 agonists weigh heavily on families. Preclinical and limited adult data suggest that cannabinoids may modulate tic expression through interactions with the endocannabinoid system, particularly via CB1 receptor activity in the basal ganglia. This phase I/II double-blind, placebo-controlled, crossover pilot trial, conducted at the Royal Children’s Hospital Melbourne and affiliated private practices and published by Groth and colleagues, enrolled 10 adolescents aged 12 to 18 with moderate-to-severe Tourette Syndrome. Participants received both an oral THC/CBD formulation (10 mg/mL THC plus 15 mg/mL CBD, titrated by weight band) and a sensory-matched placebo, each for 10 weeks, separated by a 4-week washout period.

The study met most of its primary feasibility benchmarks: 100% completion rates for study visits and blood tests, and 97.6% completion of online questionnaires among actively enrolled participants. Medication adherence, however, was acceptable in only 63.6% of participants, a clear area for protocol refinement. Dizziness was the most frequently reported adverse event, occurring in 67% of participants, though no serious adverse events were recorded and two discontinuations were evenly split between active and placebo arms. On the Clinical Global Impression of Improvement scale, three participants were rated “much improved” on medicinal cannabis versus one on placebo, but with only seven completers this observation is purely hypothesis-generating. The authors are explicit that a fully powered trial is required before any clinical recommendations can be made.

Dr. Caplan’s Take

I see families asking about cannabis for Tourette Syndrome with increasing frequency, and their frustration with existing treatment options is entirely understandable. What this study does well is establish that you can actually run a rigorous, blinded trial in this population without insurmountable barriers. That matters, because until now the conversation has been almost entirely anecdotal. But the gap between “we can study this” and “this works” is enormous, and this trial sits squarely on the first side of that divide. With seven completers, any clinical signal is noise-level at best.

In my practice, when a family raises medicinal cannabis for their teenager’s tics, I use studies like this to explain exactly where we are: early enough that we cannot make evidence-based treatment recommendations. I focus on optimizing established therapies, including Comprehensive Behavioral Intervention for Tics, and I am honest that we are watching this research space carefully but that jumping ahead of the evidence exposes young patients to real unknowns, including the adherence and dizziness challenges this very study identified.

Clinical Perspective

This study sits at the very beginning of the clinical research arc for cannabinoid-based interventions in pediatric Tourette Syndrome. It confirms that the logistical and ethical scaffolding for a proper trial can hold: blinding appears achievable with sensory-matched placebo, families are willing to enroll and engage with complex crossover protocols, and the validated outcome measures used in adult Tourette research translate to this age group. What it does not confirm, challenge, or extend is any conclusion about whether medicinal cannabis reduces tic severity, improves quality of life, or outperforms existing treatments. Clinicians should not cite this study to patients as evidence that cannabis-based products help with tics.

From a safety standpoint, the dizziness rate of 67% warrants attention, particularly given the adolescent population’s school and activity demands. The THC component raises ongoing concerns about neurodevelopmental effects with sustained use in this age group, a question this short-duration pilot was not designed to address. The suboptimal medication adherence rate suggests that taste, dosing complexity, or side effects may interfere with compliance in ways that future protocols must solve. The single most actionable recommendation for clinicians right now is to document patient and family interest in cannabinoid therapies during clinical encounters so that eligible patients can be directed toward upcoming properly powered trials as they open, rather than toward unregulated products.

Study at a Glance

Study Type

Phase I/II double-blind, placebo-controlled crossover pilot RCT

Population

Adolescents aged 12 to 18 with DSM-5 Tourette Syndrome and YGTSS Total Tic Severity score of 20 or above

Intervention

Oral THC 10 mg/mL plus CBD 15 mg/mL in MCT oil, titrated by weight band up to THC 10 or 20 mg/day, for 10 weeks

Comparator

Sensory-matched peppermint-flavored MCT oil placebo for 10 weeks

Primary Outcomes

Feasibility and acceptability of the study protocol

Sample Size

10 randomized, 7 completers

Journal

Not specified in source data

Year

Not specified in source data

DOI or PMID

Not available in source data

Funding Source

Study drug supplied by Cann Group Limited, Australia

What Kind of Evidence Is This

This is a phase I/II pilot randomized controlled trial designed to evaluate feasibility and acceptability, not clinical efficacy. It sits relatively low in the evidence hierarchy for treatment recommendations because its primary endpoints are operational metrics rather than patient-centered outcomes. The single most important inference constraint is that with 10 participants and 7 completers, no clinical outcome comparison from this study carries statistical or clinical meaning, and any apparent treatment signal must be treated as preliminary hypothesis generation only.

How This Fits With the Broader Literature

The adult Tourette literature includes a small number of randomized trials examining THC-based treatments, most notably the crossover studies by Muller-Vahl and colleagues from the early 2000s, which reported modest tic reduction with dronabinol but in samples that were similarly small. No prior registered trial has specifically examined cannabinoid therapy in adolescents with Tourette Syndrome, making this study’s contribution genuinely novel in establishing pediatric feasibility. It extends the broader trend in cannabinoid research of pilot and feasibility work preceding definitive efficacy trials, a pattern also seen in pediatric epilepsy research before the pivotal cannabidiol trials that led to regulatory approval for Dravet and Lennox-Gastaut syndromes. The current study does not challenge any established findings; rather, it fills a procedural gap that was blocking forward progress in this specific population.

Common Misreadings

The most likely overinterpretation is reading the CGI-I data, in which three participants were rated “much improved” on medicinal cannabis versus one on placebo, as preliminary evidence that cannabis-based treatment reduces tics in adolescents. This reading exceeds what the evidence supports for several reasons: the study was explicitly not powered for efficacy, the sample of seven completers makes any between-group comparison statistically meaningless, and crossover designs with inadequate washout periods can carry residual treatment or expectation effects. Reporting this finding without its feasibility framing risks creating a misleading impression of demonstrated benefit where none has been established.

Bottom Line

This pilot trial demonstrates that a rigorous, blinded, crossover study of medicinal cannabis can be conducted in adolescents with Tourette Syndrome, with good protocol completion and no serious safety signals in a very small sample. It does not establish whether medicinal cannabis reduces tics or improves outcomes in this population. Its value is infrastructural: it justifies and informs the design of a fully powered efficacy trial, which remains the necessary next step before any clinical recommendations can responsibly be made.

References

1. Groth C et al. Phase I/II pilot feasibility trial of medicinal cannabis in adolescents with Tourette Syndrome. Royal Children’s Hospital Melbourne. Study drug supplied by Cann Group Limited, Australia.
2. Muller-Vahl KR, Schneider U, Koblenz A, et al. Treatment of Tourette’s syndrome with delta 9-tetrahydrocannabinol (THC): a randomized crossover trial. Pharmacopsychiatry. 2002;35(2):57-61.
3. Muller-Vahl KR, Schneider U, Prevedel H, et al. Delta 9-tetrahydrocannabinol (THC) is effective in the treatment of tics in Tourette syndrome: a 6-week randomized trial. J Clin Psychiatry. 2003;64(4):459-465.