Chronic Pain

What it is

Chronic pain persists beyond the expected period of healing, typically defined as longer than three months. It is one of the most common chronic health conditions in adults and a leading reason patients seek medical cannabis. Chronic pain is not a single disease but a category that includes neuropathic pain (nerve-injury origin), nociceptive pain (tissue-damage origin), inflammatory pain, mixed pain (back pain, cancer pain), and centralized pain syndromes (fibromyalgia). Each subtype has a distinct evidence base for cannabis efficacy.

Cannabis and cannabis-derived therapies

The 2017 NASEM consensus report found conclusive or substantial evidence that cannabis or cannabinoids are effective for chronic pain in adults. This is the highest evidence tier in the NASEM framework. The finding has been reaffirmed by subsequent systematic reviews including the 2021 IASP (International Association for the Study of Pain) position paper, the 2022 BMJ rapid review, and the 2024 NASEM update.

Effect sizes in clinical trials are modest. Typical pain-intensity reduction is 25-30% relative to baseline, comparable to gabapentinoids, tricyclic antidepressants, and SNRIs for neuropathic pain. Cannabis is rarely a stand-alone first-line analgesic; most patients use it adjunctively with conventional therapy.

Pain subtype evidence

• Neuropathic pain: strongest evidence base. Controlled trials in HIV-associated neuropathy, diabetic peripheral neuropathy, chemotherapy-induced peripheral neuropathy, post-herpetic neuralgia, and central neuropathic pain (multiple sclerosis, spinal cord injury) have consistently shown pain reduction with both inhaled and oral preparations.
• Cancer-related pain: moderate evidence. Several trials of nabiximols (Sativex) plus opioids vs opioids alone have shown additive analgesic benefit. NCCN clinical guidelines note cannabis as one option for breakthrough cancer pain.
• Inflammatory pain: mixed evidence. Trials in rheumatoid arthritis, ankylosing spondylitis, and other inflammatory conditions have shown variable benefit, with stronger effects on sleep and quality of life than on inflammatory markers.
• Musculoskeletal pain: limited evidence at the disease level (back pain, osteoarthritis). Observational data is more positive than controlled-trial data.
• Centralized pain (fibromyalgia): limited evidence per NASEM but consistent patient-reported benefit. Several small trials have shown pain and sleep improvement.

Endocannabinoid pharmacology

Cannabis analgesia is mediated primarily through CB1 and CB2 cannabinoid receptors. CB1 receptors are densely expressed in pain-processing regions of the central nervous system (periaqueductal gray, rostral ventromedial medulla, dorsal horn of the spinal cord, and cortical pain regions). CB2 receptors are concentrated on immune cells and peripheral nerve endings where they modulate inflammatory pain signaling.

Endocannabinoids (anandamide, 2-AG) are produced on demand at active synapses. Exogenous cannabinoids from cannabis (THC, CBD, CBN, CBG, plus terpenes) interact with this system. THC is the primary analgesic component in most clinical trials; CBD has weaker direct analgesic effect but contributes through anti-inflammatory and anxiolytic mechanisms and modulates THC effects.

Cannabis form and route considerations

• Vaporization or smoking: rapid onset (minutes to peak effect), short duration (2-4 hours). Useful for breakthrough pain. Smoking carries respiratory risks; vaporization reduces but does not eliminate them.
• Sublingual tinctures and oromucosal sprays (nabiximols): intermediate onset (15-45 minutes), longer duration. Standardized dosing improves titration.
• Oral capsules and edibles: slowest onset (30 minutes to 2 hours, sometimes longer), longest duration (6-8 hours). Useful for baseline pain control. Variable absorption produces less predictable dosing.
• Topicals: localized application for musculoskeletal pain. Systemic absorption is minimal; effects are limited to the application area.
• Transdermal patches: continuous delivery; small patient population uses these but evidence is limited.

Most patients use a combination, with longer-acting baseline therapy and shorter-acting breakthrough options.

Drug interactions

Cannabis can interact with several common analgesic medication classes:

• Opioids: additive CNS depression. Combined respiratory-depression risk increases at higher doses. Some patients report reduced opioid requirement, which has both benefit (lower opioid-related side effects) and risk (potential under-treatment if cannabis effect is inconsistent).
• Gabapentinoids (gabapentin, pregabalin): additive sedation, dizziness, and cognitive impairment.
• Tricyclic antidepressants: additive anticholinergic effects, sedation, and orthostatic hypotension.
• Benzodiazepines: strong additive CNS depression.
• Warfarin: cannabis can elevate INR through CYP2C9 inhibition. Closer INR monitoring is recommended.
• Tacrolimus, cyclosporine, sirolimus: cannabis may affect serum levels through CYP3A4 and P-glycoprotein interactions.

Patients should disclose cannabis use to all prescribers, particularly during medication initiation, dose changes, or surgery.

Population considerations

• Older adults: higher sensitivity to psychoactive effects; lower starting doses recommended. Fall risk and cognitive interaction with polypharmacy require careful monitoring.
• Pregnancy and breastfeeding: cannabis is contraindicated. THC crosses the placenta and is excreted in breast milk; observational data link maternal cannabis use to lower birth weight and developmental concerns.
• Pediatric patients: very limited evidence for chronic pain in children; cannabis use in this population is restricted to specific qualifying conditions (e.g., severe seizure disorders, cancer).
• Patients with active substance use disorder: require careful screening. History of cannabis use disorder is a relative contraindication.
• Patients with psychiatric history: cannabis can precipitate or worsen psychosis in susceptible individuals; history of psychotic disorder or family history of psychotic disorder warrants caution.

Long-term use considerations

Long-term cannabis use carries documented risks:

• Cannabis use disorder: affects roughly 9% of adult users overall; higher in adolescent-onset use (~17%) and daily users (25-30%). Withdrawal syndrome includes irritability, sleep disturbance, appetite reduction, and craving.
• Respiratory effects: chronic smoking is associated with bronchitis symptoms and impaired pulmonary function. Vaporization reduces these but does not eliminate them.
• Cognitive effects: acute intoxication impairs working memory, attention, and reaction time. Long-term effects on cognition in adult users are debated; adolescent-onset use shows more durable effects.
• Tolerance: dose escalation is common with regular use. Periodic dose holidays can reset tolerance.

Practical guidance

Patients should coordinate cannabis use with their pain-management physician, primary care provider, and any other prescriber. Start with the lowest effective dose, titrate slowly, and document symptom response. Do not substitute cannabis for prescribed disease-modifying therapy. Driving or operating heavy equipment while acutely impaired by cannabis is contraindicated and may carry criminal-law exposure regardless of medical authorization.

Related conditions

Several related conditions in the mmjnow library overlap with chronic pain: peripheral-neuropathy, fibromyalgia, multiple-sclerosis-spasticity, spinal-cord-injury, cancer, hiv-aids, sickle-cell-disease, rheumatoid-arthritis, migraine, crohns-disease, and inflammatory-bowel-disease all involve chronic-pain components for which cannabis evidence has been studied.