Cannabis and pain: what the evidence supports

Pain is the most common reason adults give for using cannabis medically, and it is the area with the most research behind it. It is also where the gap between what the studies show and what the internet claims is at its widest. Both halves of that are worth saying.

Where the evidence is strongest

The best-supported use is chronic neuropathic pain — pain caused by damage to the nerves themselves, as in diabetic neuropathy, nerve injury, or some conditions of the spinal cord. Across a good number of trials, cannabis and cannabis-based medicines produce a real but modest improvement over placebo, and a modest average conceals the useful truth: some people get a great deal from it and others get very little.

Two other areas have reasonable support: spasticity in multiple sclerosis, where cannabis-based medicines are prescribed in a number of countries, and pain accompanying some cancers, particularly where other approaches have been exhausted.

Where it is thin

• Acute pain — a broken bone, a fresh injury, pain after surgery — has little evidence behind cannabis and some suggesting it does not help much at all. It is not an analgesic in the way a painkiller is.
• Everyday musculoskeletal pain — a bad back, an arthritic knee — is where a great deal of anecdote lives and much less good evidence. That does not mean people are imagining relief. It means the studies that would settle it have largely not been done well enough.

The part people describe that studies struggle to measure

Ask somebody with long-standing pain what cannabis does for them and the answer is very often not "it is gone". It is that the pain bothers them less, that they sleep through the night, that they stop bracing against it. Pain has an emotional dimension as much as a sensory one, and it is plausible that this is where much of the benefit sits. That is a real thing to gain, and it is hard to capture in a scale from nought to ten.

The trade-offs, said plainly

Nothing useful is free.

• Effects come with the rest of the effects: sedation, altered thinking, dry mouth, and for some people anxiety. Daytime use has to be weighed against needing to work, drive or care for somebody — see cannabis, driving and work.
• Tolerance builds against pain relief as it does against everything else, and the answer is a break rather than a bigger dose.
• Smoking anything is hard on the lungs. For a daily user managing a long-term condition, that matters more than for an occasional one.
• Cannabis interacts with medicines, and people in pain are frequently on several. That conversation belongs with a pharmacist or doctor, not a forum.

How people who do well with it tend to go about it

Low amounts, taken deliberately, adjusted from what actually happened rather than from hope — the microdosing approach, essentially. A written note of what was taken and what changed, because pain varies day to day for reasons that have nothing to do with what you took, and memory quietly rewrites the record. And an honest review after a few weeks: is this doing something, or am I simply used to it now?

The one thing to take away

Cannabis is a plausible option for some kinds of chronic pain, particularly nerve pain, with a real but moderate expected benefit — not a cure, not a replacement for a diagnosis, and not something to start on your own while carrying a condition and a shelf of medication. Tell the professional treating you what you are using. They have almost certainly heard it before, and they cannot account for what they do not know about.