Medical Cannabis for Chronic Pain: What Does the Evidence Say?

Chronic pain — defined as pain lasting more than three months — affects an estimated 28 million adults in the UK, representing around 43% of the population. It is the leading cause of disability worldwide and places an enormous burden on both individuals and the NHS.

Conventional treatments including opioids, NSAIDs, antidepressants, and anticonvulsants are effective for many patients, but a significant proportion experience inadequate relief or intolerable side effects. It is for this group that cannabis-based medicinal products (CBMPs) have attracted the most clinical interest.

To understand how CBMPs work for pain, it helps to understand the endocannabinoid system (ECS). The ECS is a complex cell-signalling system present throughout the body that plays a key role in regulating pain, inflammation, mood, sleep, and immune function.

The two primary cannabinoids in CBMPs — THC (tetrahydrocannabinol) and CBD (cannabidiol) — interact with the ECS in different ways. THC binds directly to CB1 receptors in the brain and nervous system, producing analgesic (pain-relieving) and anti-inflammatory effects. CBD modulates the ECS more indirectly, reducing inflammation and anxiety without producing the psychoactive effects associated with THC.

The evidence base for CBMPs in chronic pain has grown substantially over the past decade. Key findings include:

• A 2018 systematic review published in the Journal of Clinical Medicine found that CBMPs were associated with significant reductions in pain scores across multiple chronic pain conditions.

• The UK Medical Cannabis Registry, which tracks real-world patient outcomes, reported that 64% of patients with chronic pain experienced clinically significant reductions in pain after six months of CBMP treatment.

• A 2022 meta-analysis in JAMA Network Open found that cannabinoids were associated with greater odds of achieving a 30% reduction in pain compared to placebo.

• Evidence is particularly strong for neuropathic pain (nerve pain), where conventional treatments often fail.

The evidence is strongest for the following chronic pain conditions:

Neuropathic pain — including diabetic neuropathy, post-herpetic neuralgia, and central sensitisation syndromes. Multiple randomised controlled trials have demonstrated significant pain reduction.

Multiple sclerosis spasticity — Sativex (nabiximols), a cannabis-derived oromucosal spray, is the only CBMP with a UK marketing authorisation, specifically for MS spasticity.

Cancer-related pain — particularly where conventional opioid therapy is inadequate or causing unacceptable side effects.

Fibromyalgia — emerging evidence suggests CBMPs may reduce pain, improve sleep, and enhance quality of life in fibromyalgia patients.

One of the most significant potential benefits of CBMPs in chronic pain management is their ability to reduce opioid use. The UK opioid crisis — with prescriptions of strong opioids having increased by 34% over the past decade — represents a major public health challenge.

Several observational studies have found that patients who begin CBMP treatment significantly reduce their opioid consumption. A 2019 study in the European Journal of Internal Medicine found that 44% of patients using medical cannabis were able to reduce or stop opioid use entirely. This opioid-sparing effect is considered one of the most clinically important potential benefits of CBMPs.

CBMPs are not without risks. Common side effects include dizziness, fatigue, dry mouth, and cognitive effects. High-THC products carry a risk of anxiety, paranoia, and psychological dependence with long-term use.

However, under medical supervision with appropriate dosing and monitoring, these risks are manageable. CBD-dominant products carry a significantly lower risk profile. Your prescribing clinician will discuss the risk-benefit balance with you based on your specific situation.