Spain Study Finds Cannabis Reduces Restless Legs Syndrome Symptoms

Study Design and Patient Cohort

Researchers enrolled 127 adults diagnosed with moderate-to-severe RLS and tracked self-reported cannabis use alongside standardized symptom assessments. The cohort included 78 women and 49 men, median age 54. All had failed at least one first-line pharmaceutical intervention—dopamine agonists or gabapentinoids. Participants weren't assigned cannabis; they self-selected use patterns, making this an observational rather than randomized controlled trial.

Symptom severity was measured using the International Restless Legs Syndrome Study Group Rating Scale (IRLS), a validated 40-point instrument. Baseline median score: 28 (severe range). Assessments occurred at enrollment, month 3, and month 6.

THC-Dominant Cultivars Showed Strongest Symptom Reduction

Patients using cultivars with THC concentrations above 15% reported a median 42% reduction in IRLS scores at six months, compared to 19% among CBD-only users. The most commonly consumed cultivars were:

• Gorilla Glue #4 (22-25% THC, <1% CBD) — 31 patients, median IRLS drop of 12 points
• Northern Lights (18-21% THC, <1% CBD) — 24 patients, median drop of 11 points
• ACDC (1-6% THC, 14-20% CBD) — 18 patients, median drop of 5 points

Terpene profiles weren't controlled. Patient diaries noted frequent mentions of myrcene-dominant strains correlating with improved sleep onset, but no formal terpene assays were conducted.

The data suggest THC's sedative and muscle-relaxant properties may address the motor and sensory components of RLS more directly than CBD's anti-inflammatory pathways alone.

Dosing Patterns and Administration Routes

Median effective dose among responders was 12 mg THC consumed 60-90 minutes before bed, most commonly via vaporization or sublingual tincture. Smoking was the least effective route. Patients reported faster onset but shorter duration of relief. Edibles (10-15 mg THC capsules) produced the longest symptom suppression but required earlier dosing due to delayed onset.

Fourteen patients reported tolerance buildup after four months, requiring dose escalation to 18-20 mg to maintain efficacy. No serious adverse events were recorded. Twenty-two percent of participants reported next-day grogginess at doses above 15 mg.

Limitations and Next Steps

The study's observational design prevents causal claims, and the lack of a placebo control leaves open the possibility of expectancy effects. Researchers noted that patients who chose cannabis may differ systematically from those who didn't—selection bias is a known confound in self-directed treatment studies.

What comes next? The University of Barcelona team is now designing a randomized, placebo-controlled trial comparing a standardized 15 mg THC tincture against a CBD isolate and a true placebo. Enrollment is expected to begin in Q1 2027. For full background on cannabis research in movement disorders, see the CannIntel topic hub on cannabis and restless legs syndrome.