Cannabis and Chronic Pain: What the Evidence Shows — So Far

 

Cannabis As Schedule III 

Cannabis and Chronic Pain: What the Evidence Shows

Note on the evidence: For decades, cannabis research in the United States was constrained by its classification as a Schedule I substance, limiting access, funding, product consistency, and long-term clinical trials. With marijuana now moved to Schedule III, many of the most rigorous studies have only just become feasible. The findings summarized below reflect the best evidence available to date — not the full scope of what future research may reveal.

TL;DR

• Cannabis and cannabinoids show modest pain relief, strongest for neuropathic chronic pain.
• Major reviews (including the 2017 National Academies report) find cannabis is more effective than placebo for chronic pain, but effects are generally small.
• Benefits vary by product, dose, and delivery method, with inhaled and THC-containing products showing stronger effects.
• Adverse effects are usually mild and short-term (e.g., dizziness, dry mouth, nausea).
• Evidence quality is moderate; larger and longer-term studies are still needed.

Several key studies and systematic reviews have examined the use of cannabis or cannabinoids for chronic pain, particularly neuropathic pain. Overall, the evidence suggests modest benefits, with outcomes varying by formulation, route of administration, and pain type.

Landmark Review

The 2017 National Academies of Sciences, Engineering, and Medicine (NASEM) report concluded that there is substantial evidence that cannabis or cannabinoids are effective for treating chronic pain in adults. Based on a comprehensive review of existing trials, the report found that patients treated with cannabinoids were more likely to experience a clinically significant reduction in pain symptoms compared to placebo. This report is frequently cited as a benchmark in cannabis research.

Major Systematic Reviews and Meta-Analyses

• 2021 BMJ Systematic Review and Meta-Analysis: Analyzed 32 randomized controlled trials (RCTs) involving over 5,000 patients with chronic non-cancer and cancer-related pain. The review found moderate- to high-certainty evidence that non-inhaled medical cannabis or cannabinoids provided small to very small improvements in pain relief (e.g., higher likelihood of achieving ≥30% pain reduction), physical functioning, and sleep quality compared to placebo. Transient adverse effects such as dizziness and nausea were more common.
• 2017 Meta-Analysis (Aviram et al.): Reviewed 43 RCTs and found cannabis-based medicines were associated with pain reduction, particularly for neuropathic pain and when administered via inhalation. However, overall effects were limited, and gastrointestinal side effects were more frequent with oral formulations.
• AHRQ Living Systematic Review (updated 2025): Synthesizes placebo-controlled RCTs and observational studies. Findings indicate small benefits for pain severity with high-THC products, though overall certainty remains low due to short study durations, product variability, and methodological limitations.
• 2018 Meta-Analysis (Stockings et al.): Reviewed 104 studies and reported a small but statistically significant effect for achieving ≥30% pain reduction (number needed to treat: 24). Evidence was strongest for neuropathic pain, but adverse events were more common (number needed to harm: 6).

Specific RCTs and Notable Findings

Evidence is strongest for neuropathic pain, including pain related to multiple sclerosis, HIV, and diabetes:

• Trials of nabiximols (THC:CBD oromucosal spray, such as Sativex) in multiple sclerosis–related neuropathic pain demonstrated significant reductions in pain intensity and improvements in sleep quality.
• Inhaled cannabis trials (e.g., Wilsey et al., 2008 and 2013) showed dose-dependent relief of neuropathic pain, with many patients achieving greater than 30% reductions in pain scores.
• A phase 3 randomized controlled trial (2025) of a full-spectrum cannabis extract (VER-01) for chronic low back pain reported reductions in pain severity, improved physical function, and better sleep outcomes, without evidence of dependence.

For other chronic pain conditions such as fibromyalgia and cancer-related pain, results are mixed or limited, with several trials showing no significant benefit compared to placebo.

Overall Assessment

Across meta-analyses, cannabinoids appear to offer modest relief primarily for neuropathic chronic pain, typically corresponding to an average reduction of approximately 3–10 mm on a 100 mm visual analog pain scale. Benefits are often short-term, and the overall quality of evidence is moderate due to small sample sizes, short trial durations, and variability in cannabis products.

Adverse effects are usually mild and transient, including dizziness, dry mouth, nausea, and cognitive changes. More large-scale, long-term randomized controlled trials are needed to clarify optimal dosing, formulations, and effectiveness for specific pain conditions.

For clinical decision-making, consultation of recent professional guidelines (such as those from BMJ or relevant medical societies) is recommended.