Small Pilot Trial Finds Medicinal Cannabis Feasible to Study in Adolescents with Tourette Syndrome, But Efficacy Remains Unknown

A ten-person crossover study of THC and CBD oil in adolescents with Tourette Syndrome establishes that a larger, fully powered randomized controlled trial is logistically possible and acceptable to families, but the sample is far too small to draw any conclusions about whether the treatment actually reduces tics.

Why This Matters

Tourette Syndrome affects roughly 1% of school-age children, and available pharmacotherapies carry significant side-effect burdens that limit adherence and quality of life. Cannabis-based medicines have shown preliminary signals in small adult studies, but until now, no registered clinical trial had examined their use in children or adolescents with this condition. The absence of any structured pediatric data has left clinicians unable to counsel families who increasingly ask about cannabis, making this first feasibility dataset an important step toward closing a genuine evidence gap.

Clinical Summary

Tourette Syndrome in adolescents often proves refractory to first-line agents such as alpha-2 agonists and antipsychotics, driving families toward alternative treatments including cannabis products. This phase I/II double-blind, placebo-controlled crossover pilot trial, conducted at the Royal Children’s Hospital in Melbourne, Australia, randomized ten adolescents aged 12 to 18 with moderate-to-severe tic severity to receive either a whole-plant cannabis oil containing THC (10 mg/mL) and CBD (15 mg/mL) or a peppermint-flavored MCT oil placebo for a 10-week treatment period, followed by a 4-week washout and crossover. The mechanistic rationale rests on the established presence of cannabinoid CB1 receptors in the basal ganglia, a circuit implicated in tic generation, along with preclinical evidence suggesting endocannabinoid modulation of dopaminergic signaling in the striatum.

The primary findings concern logistics, not treatment effect. Protocol adherence was strong: 100% visit completion, 100% blood test completion, and 97.6% online questionnaire completion among enrolled participants. Parents rated the study design acceptable. However, three of ten participants did not complete the full protocol, including two who discontinued due to adverse events and one lost to follow-up, yielding a 30% non-completion rate. Dizziness was reported in 67% of participants, and no serious adverse events occurred. On the exploratory Clinical Global Impression-Improvement scale, three participants were rated “much improved” during the cannabis period versus one during placebo, but with only seven completers this numerical difference is statistically uninterpretable. The authors explicitly state that a fully powered study is needed before any efficacy conclusions can be drawn.

Dr. Caplan’s Take

This study does exactly what it says on the label: it tests whether a rigorous crossover trial of cannabis in teenagers with Tourette Syndrome can actually be run. The answer is encouraging. The adherence numbers are solid, the blinding held, and parents were willing to enroll their children. But what this study does not do, and cannot do with seven completers, is tell us whether the treatment helps. That distinction matters enormously because families come into clinic having already read headlines that blur feasibility with proof. When a parent asks me whether cannabis works for their child’s tics, an honest answer right now is that we still do not know.

In practice, I take these conversations seriously and do not dismiss them. I explain that the adult evidence base is thin, the adolescent evidence base is essentially this single pilot, and the 67% dizziness rate is a real consideration in a school-age population. For patients with tics refractory to established therapies, I focus on optimizing behavioral interventions such as Comprehensive Behavioral Intervention for Tics, ensure we have exhausted evidence-supported pharmacological options, and document the conversation about cannabis so that if a powered trial opens, the family is positioned to participate.

Clinical Perspective

This pilot sits at the very beginning of the research arc for cannabinoid-based treatment of pediatric Tourette Syndrome. It confirms that families are willing to participate in placebo-controlled cannabis research involving their children, which had been an open question, and it demonstrates that the crossover design with a 4-week washout is operationally manageable. It does not confirm, challenge, or even meaningfully engage with the question of efficacy. Clinicians should recognize that the exploratory CGI-I numbers provide no basis for altering treatment recommendations. The 30% non-completion rate is itself a finding that warrants attention: any future trial will need robust retention strategies, particularly given that two withdrawals were adverse-event driven.

From a pharmacological standpoint, the THC component raises standard concerns about cognitive effects in the developing adolescent brain, and the 67% incidence of dizziness is clinically relevant for a population attending school and participating in physical activities. Drug interactions with concurrent tic medications, particularly antipsychotics that also act on dopaminergic pathways, remain uncharacterized in this age group. Clinicians should document any patient or family interest in cannabis-based treatment, monitor for unsupervised use of commercial cannabis products, and refer eligible patients to any emerging registered trials rather than endorsing off-protocol use.

Study at a Glance

Study Type

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

Population

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

Intervention

THC 10 mg/mL plus CBD 15 mg/mL whole-plant oil, titrated to a maximum of THC 10 mg/day (under 50 kg) or 20 mg/day (50 kg or above), over a 10-week treatment phase

Comparator

Peppermint-flavored MCT oil placebo

Primary Outcomes

Feasibility and acceptability metrics including visit completion, blood test completion, questionnaire completion, medication adherence, and parent acceptability ratings

Sample Size

10 randomized; 7 completed full protocol

Setting

Single site, Royal Children’s Hospital, Melbourne, Australia

Journal

Not specified in extracted data

Year

2025

DOI or PMID

Not available in extracted data

Funding Source

Study drug supplied by Cann Group Limited, Australia

What Kind of Evidence Is This

This is an original phase I/II double-blind, placebo-controlled crossover pilot randomized controlled trial. Pilot feasibility trials occupy a position in the evidence hierarchy below powered confirmatory RCTs: they are designed to test whether a full-scale study can be conducted, not to determine whether a treatment works. The most important inference constraint is that no efficacy conclusion, positive or negative, is permissible from a study of seven completers that was never powered to detect a treatment effect.

How This Fits With the Broader Literature

The adult literature on cannabis and Tourette Syndrome is itself limited, resting primarily on a small German crossover trial by Muller-Vahl and colleagues (2002) using oral THC in 12 adults, and a subsequent short parallel-group trial by the same group (2003) in 24 adults. Both suggested possible tic reduction but had significant methodological limitations. A more recent Australian crossover trial in adults (2023) added modestly to this base. This adolescent pilot extends the research trajectory into a new population where no prior registered trial data existed, confirming that controlled research is operationally possible. It does not yet add to the efficacy evidence base in any interpretable way and should be understood as a methodological stepping stone rather than a clinical finding.

Common Misreadings

The most likely overinterpretation is treating the exploratory CGI-I result, where three participants improved on cannabis versus one on placebo, as preliminary evidence that the treatment works. This reading exceeds what the data support for several reasons: the comparison involves only seven completers, no inferential statistics were applied or would be meaningful at this sample size, the crossover design introduces potential period and carryover effects, and the authors themselves label these outcomes as hypothesis-generating only. Citing this numerical trend as a “signal of efficacy” in clinical or media contexts would misrepresent the study’s purpose and findings.

Bottom Line

This pilot trial demonstrates that a rigorous placebo-controlled crossover study of medicinal cannabis is logistically feasible and acceptable to adolescents with Tourette Syndrome and their families. It does not establish whether the treatment reduces tics. The 67% dizziness rate and 30% non-completion rate are important signals for future trial design. Until a fully powered efficacy trial is completed, clinicians have no adolescent-specific evidence to support recommending cannabis-based treatment for tics.

References

1. 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. DOI: 10.1055/s-2002-25028
2. 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. DOI: 10.4088/JCP.v64n0417
3. Current study: Phase I/II double-blind, placebo-controlled crossover pilot RCT of medicinal cannabis (THC+CBD) in adolescents with Tourette Syndrome. Royal Children’s Hospital, Melbourne, Australia. 2025. Full citation details not available in extracted data.