The short answer
Cannabis can lower chronic pain for some people. Evidence is strongest for nerve pain from neuropathy, pain from multiple sclerosis, and cancer pain. Evidence for acute pain from injury or surgery is weak. No cannabis product is approved by the FDA to treat pain.
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What the research shows
A 2017 review by the National Academies of Sciences, Engineering, and Medicine looked at more than 10,000 studies. It found substantial evidence that cannabis relieves chronic pain in adults. The same report found substantial evidence for MS spasticity and modest evidence for sleep problems.
A 2015 meta-analysis in JAMA reviewed 79 trials with 6,462 patients. It found moderate-quality evidence for cannabinoids in chronic pain. More patients on cannabinoids reported a 30% or larger drop in pain scores than patients on placebo.
THC, CBD, and the endocannabinoid system
THC binds CB1 receptors in the brain and spinal cord. CB1 activation changes pain signaling and causes the high. CBD binds CB1 with low affinity. CBD may lower inflammation and may slow the breakdown of anandamide, a natural cannabinoid. CBD does not cause intoxication.
Most clinical pain data comes from products that contain both THC and CBD, including nabiximols. That oromucosal spray is approved in Canada and parts of Europe. It is not sold in the US.
Forms and timing
- Inhaled flower or vape: effects in 2 to 10 minutes, peak at 15 to 30 minutes, last 2 to 3 hours.
- Oral edibles, capsules, tinctures: effects in 30 to 120 minutes, peak at 2 to 4 hours, last 4 to 8 hours.
- Topical: little THC reaches the bloodstream. Evidence for pain relief is limited.
Taking a second oral dose before the first one takes effect is a common cause of a bad reaction.
Dosing
Start low. A common starting dose is 1 to 2.5 mg THC, taken once. Wait at least 2 hours for oral products before adding more. Raise the dose in small steps every few days. Keep the THC to CBD ratio fixed while you titrate. Track pain scores, dose, and side effects in a note.
CBD doses in pain trials ranged from tens of milligrams to more than 1,000 mg per day. There is no standard dose for pain.
Risks and side effects
Common effects: dizziness, dry mouth, drowsiness, slower reaction time, and short-term memory problems. Cannabis impairs driving for several hours after use. Repeated vomiting after long-term heavy use can signal cannabinoid hyperemesis syndrome. Stop use and get care.
About 3 in 10 people who use cannabis develop cannabis use disorder, per the National Institute on Drug Abuse. Risk is higher for people who start before age 18.
CBD and THC interact with drugs that use CYP450 enzymes, including warfarin, clobazam, and some statins. Tell your clinician about all medications.
Talk to a clinician
Bring your medication list. Ask about interactions. Keep a record of dose and effect. Do not stop prescribed pain treatment on your own.
Legal status and product labels
State law varies. Medical cannabis is legal in most US states and adult use in many. Label accuracy is not guaranteed. Third-party lab tests give THC and CBD content per batch.