A Phase 2 interventional study of CBD Oral Solution and Placebo in Fragile X Syndrome, sponsored by Université de Sherbrooke. Recruiting at 1 site in Canada. Open to participants aged 7 Years to 40 Years. Per ClinicalTrials.gov, last updated 2026-08-28.
Sponsored by Université de Sherbrooke · Phase 2, Interventional, and Treatment
This study focuses on the therapeutic relevance of the endocannabinoid (eCB) system for the treatment of Fragile-X syndrome (FXS), the primary hereditary cause of autism spectrum disorder (ASD). Most individuals with FXS have moderate to severe intellectual disability (ID), and caregivers are mainly concerned about aggressive behavior and anxiety problems. Since FXS individuals have a normal lifespan, the overall lifetime cost for the Canadian society of a single case is estimated at $1.2 to $4.7 millions reaching $18 billions for all FXS cases. There is no cure for FXS, as all clinical trials so far have been unsuccessful.FXS is caused by transcriptional silencing of the Fragile X mental retardation protein (FMR1) gene, making FXS a simple model to study ASD and ID pathophysiological mechanisms. Of those, neuronal hyperexcitability is largely recognized as a core deficit in FXS, and a critical therapeutic target for the disorder. Using transcranial magnetic stimulation (TMS) in FXS patients, our team provided the first direct evidence of Gamma-aminobutyric acid (GABA) receptor a (GABAa) dysfunctions in humans with this disorder and showed that this inhibitory deficit is linked with cortical hyperexcitability (PMID: 31748507). Concurrent lines of evidence suggest that stimulation of the endocannabinoid (eCB) system with the administration of Cannabidiol (CBD) could upregulate GABAergic function and correct inhibitory deficits presumed responsible for the neuropsychiatric phenotype of FXS. CBD has been shown to increase GABA concentration levels in the brains of healthy individuals, an effect that could help correct the hyperexcitability typically found in FXS. Thus, this trial aims to define the therapeutic potential of the eCB system for FXS, by measuring the impacts of oral CBD administration on the principal inhibitory neurotransmitter system of FXS patients, and the severity of the clinical phenotype.
114 studies on the registry are indexed under Fragile X Syndrome; 24 are open to participants now.
This study's planned enrollment of 40 is below the median of 50 across 91 interventional studies indexed under Fragile X Syndrome.
Browse Fragile X Syndrome studies →Université de Sherbrooke is the lead sponsor of 295 studies on the registry; 65 are open to participants now.
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Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Two enzymes measured in a routine blood test of the liver. Higher levels can mean the liver is under strain or damaged. SGPT and SGOT are older names for ALT and AST.
Criteria usually give a limit as a multiple of the upper limit of normal (ULN), often higher when cancer has spread to the liver.
A yellow substance made when red blood cells are broken down, which the liver clears. A high level can mean a problem with the liver or the bile ducts.
Criteria often allow more for people with Gilbert’s syndrome, a harmless inherited condition that raises bilirubin.
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
ALT and AST (liver enzymes)
Two enzymes measured in a routine blood test of the liver. Higher levels can mean the liver is under strain or damaged. SGPT and SGOT are older names for ALT and AST.
Criteria usually give a limit as a multiple of the upper limit of normal (ULN), often higher when cancer has spread to the liver.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Bilirubin
A yellow substance made when red blood cells are broken down, which the liver clears. A high level can mean a problem with the liver or the bile ducts.
Criteria often allow more for people with Gilbert’s syndrome, a harmless inherited condition that raises bilirubin.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Contraindication
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Participants will start with CBD to stimulate the eCB for 12 weeks, undergo an 8-week washout period, and then receive a 12-week placebo.
Drug: CBD Oral Solution · Drug: Placebo
Participants will start with a placebo for 12 weeks, undergo an 8-week washout period, and then receive a 12-week CBD to stimulate the eCB system.
Drug: CBD Oral Solution · Drug: Placebo
Participants will start with oral CBD dose of 5 mg/kg/day for two weeks and then increase to 10 mg/kg/day.
Participants will receive a dose of a placebo composed of the inactive ingredients of CBD of the same volume as the CBD Oral Solution.
Impact of Oral CBD Solution anxiety.
Caregivers will complete The Anxiety, Depression, and Mood Scale (ADAMS). The ADAMS consists of 29 items on a 4-point scale from 0 (behavior have not occurred or is not a problem) to 3 (behavior occurs a lot, or is a severe problem). It evaluates emotional disturbances along five dimensions: mania/hyperactivity, depressed mood, social avoidance, general anxiety, and obsessive behavior.
Time frame: At baseline, 12 weeks, 20 weeks, and 32 weeks
Impact of Oral CBD Solution on disruptive behavior
Caregivers will complete the Aberrant Behavior Checklist-Community Fragile-X (ABC-C FX). The ABC-C FX has 55 items and is subdivided into explores 6 subdomains: irritability, hyperactivity, lethargy/withdrawal, stereotypy, inappropriate speech, and social avoidance. Higher scores reflect higher aberrant behavior. ABC-C FX is considered the gold standard for assessing behavioral changes in clinical trials in FXS.
Time frame: At baseline, 12 weeks, 20 weeks, and 32 weeks
Impact of Oral CBD Solution on Behavioral Inhibition
Participants will complete the NIH Toolbox Cognitive Battery Flanker Task, a behavioral inhibition task validated in FXS. Global scores range from 0 to 10 and are algorithmically defined using accuracy and reaction time. Higher scores reflect better performance.
Time frame: At baseline, 12 weeks, 20 weeks, and 32 weeks
Impact of Oral CBD Solution on intracortical inhibition
TMS-derived measure of Intracortical inhibition: The degree of decrease of peak-to-peak motor evoked potential (MEP) amplitude induced by the administration of a conditioning stimulus (set at 70% of resting motor threshold) 2-4 ms before the test stimulus (stimulation intensity required to produce an MEP of 1 millivolt (mV), approximately 120% of resting motor threshold)
Time frame: At baseline, 12 weeks, 20 weeks, and 32 weeks
Impact of Oral CBD Solution on intracortical facilitation
Transcranial magnetic stimulation (TMS) -derived measure of Intracortical facilitation: The degree of increase of peak-to-peak motor evoked potential (MEP) amplitude induced by the administration of a conditioning stimulus (set at 80% of resting motor threshold) 12-24 ms before the test stimulus (stimulation intensity required to produce an MEP of 1 mV, approximately 120% of resting motor threshold).
Time frame: At baseline, 12 weeks, 20 weeks, and 32 weeks
Impact of Oral CBD Solution on
Estimation of GABA concentrations in the brain from magnetic resonance spectroscopy
Time frame: At baseline, 12 weeks, 20 weeks, and 32 weeks
Plan to share: No
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Started Sep 2025 (actual). Primary completion is estimated for Jul 2028, 34 months after the start.
Of 15 phase 2 interventional studies under Fragile X Syndrome, half reached primary completion within 24 months of starting (the median), counting those still running; a quarter within 15 and three quarters within 37. This study's planned 34 months is above that.
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Studies of the drug tested here: Cannabidiol