Short answer
Most research on cannabis and muscle spasms comes from multiple sclerosis (MS). Randomized trials of oral cannabis extract, THC, and nabiximols (a THC and CBD spray) show a drop in patient-reported spasticity and spasm counts. The same trials show no change on the Ashworth scale, which a clinician scores. Evidence for spinal cord injury, cerebral palsy, and other causes of spasm is small and mixed.
What the studies measured
Spasticity and spasm are not the same. Spasticity is a speed-dependent rise in muscle tone. A spasm is a sudden involuntary contraction. Trials split outcomes into two groups:
- Patient-reported scales. Examples: the 0 to 10 spasticity numeric rating scale and spasm frequency counts.
- Clinician-rated scales. Example: the Ashworth scale, which grades resistance to passive movement.
Cannabis products moved the first group in most trials and the second group in few.
cannabis for muscle spasticity relief
Key trials
A 2010 trial in the United Kingdom enrolled 279 people with MS. The primary outcome was the Ashworth score. It did not differ between cannabis extract and placebo. Patient-reported spasticity improved by a small amount. A 2011 trial of 241 people with MS reported a larger drop on the spasticity rating scale with nabiximols than with placebo. A 2015 meta-analysis in JAMA pooled 79 trials and rated the evidence for MS spasticity as moderate quality. A 2022 Cochrane review reached a similar conclusion.
Topicals for Muscle Spasms Guide
Nabiximols
Nabiximols is an oromucosal spray. Each spray delivers 2.7 mg THC and 2.5 mg CBD. The labeled maximum is 12 sprays per day. Regulators in Canada, the United Kingdom, Germany, and Spain approved it as an add-on for MS spasticity. The US Food and Drug Administration has not approved it. No cannabis product carries an FDA indication for spasm or spasticity.
How THC acts on muscle tone
THC is a partial agonist at CB1 and CB2 receptors. CB1 receptors sit in the brain, spinal cord, and peripheral nerve endings. In the spinal cord they adjust the firing of motor neurons and the release of excitatory signals. CBD binds CB1 with low affinity and acts on other targets, including TRPV1. The chain from receptor to reduced spasm is not mapped.
Dose and side effects
Trials titrated doses over 1 to 2 weeks. Reported side effects:
- Dizziness
- Drowsiness and fatigue
- Dry mouth
- Impaired balance
- Problems with memory and attention
These effects matter for driving and for tasks that need coordination. THC also adds to the sedation from alcohol, benzodiazepines, and opioids.
Limits of the evidence
Sample sizes are small. Most trials ran 4 to 15 weeks. Outcomes depend on self-report, and blinding is hard when a product causes a noticeable high. Data on spinal cord injury spasticity come from a few small trials with mixed results. Researchers have not settled a dose, a ratio of THC to CBD, or a way to predict who responds.
This is a summary of published research. It is not medical advice.