Cannabis for Back Muscle Spasms: Evidence, Doses, Risks

Cannabis may relax muscles. No cannabis product is FDA approved to treat back muscle spasms. Evidence for THC and CBD in back spasm is thin. Most muscle spasm data comes from multiple sclerosis trials, not from low back pain trials.

Cannabis Dosage for Muscle Spasms: Start Low, Go Slow

What the research covers

• MS spasticity. Nabiximols (a THC and CBD oromucosal spray) and oral THC lowered spasticity scores by a small amount in trials. Patients reported less stiffness. Muscle strength and function often stayed the same.
• Chronic pain. Cochrane reviews rate cannabinoid evidence as low to moderate quality. Effect sizes are small.
• Low back pain. Few trials exist. Most studies mix back pain with other pain types. No large trial isolates back muscle spasm.

How THC and CBD act

THC binds CB1 receptors in the brain and spinal cord. CB1 receptors sit on neurons that signal muscle contraction. CBD binds CB1 with low affinity. CBD may affect serotonin receptors and inflammation. A muscle relaxation mechanism for CBD is not established.

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Muscle relaxants approved for back spasm include cyclobenzaprine, tizanidine, baclofen, metaxalone, and carisoprodol. These act on the central nervous system.

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Forms and onset

• Inhaled. Onset 1 to 5 minutes. Effect lasts 1 to 3 hours.
• Oral. Onset 30 to 120 minutes. Effect lasts 4 to 8 hours. Slow onset causes most cases of overdose.
• Topical. No psychoactive effect. Evidence for muscle spasm is minimal.

Average THC in US retail flower rose from about 4% in 1995 to about 15% in 2021, per NIDA data. Some products test above 30%.

Dose

Start low. 2.5 mg THC by mouth is a common starting dose in state medical programs. Wait 2 hours before taking more. CBD doses in trials range from 5 mg to 50 mg per kg per day. No standard dose exists for back spasm. Potency labels vary, so ask for a certificate of analysis.

Risks and interactions

• Side effects include drowsiness, dizziness, dry mouth, fast heart rate, impaired coordination, and anxiety.
• CDC data put cannabis use disorder at about 3 in 10 people who use cannabis. Risk is higher for people who start in their teens.
• CBD inhibits CYP2C19 and CYP3A4. It can raise blood levels of clobazam, warfarin, and some statins.
• Do not drive after use. THC impairs reaction time for 3 to 5 hours.
• Federal law lists cannabis as Schedule I. States run their own medical and adult use programs. A clinician cannot prescribe it at the federal level.

What to ask a clinician

• Is the spasm from strain, disc injury, spinal stenosis, or spondylolisthesis? Treatment differs for each.
• Would physical therapy or a standard muscle relaxant be a better first step?
• How does cannabis interact with current prescriptions?

Bottom line

Evidence is limited. Small trials show modest relief in MS spasticity. No trial shows cannabis resolves back muscle spasm. NSAIDs, muscle relaxants, and physical therapy have more supporting data.