Injecting Cannabinoids Directly Into Muscles Reduced Pain in Rats | Research

The takeaway

Both CB1 and CB2 cannabinoid receptor agonists reduced muscular pain in rats, with local injection into the muscle being more effective than systemic administration in one of two pain models.

Read this if you deal with muscle pain and are curious about targeted cannabinoid approaches.

Local injection was more effective than systemic in the gastrocnemius pain model

What the researchers found

Researchers tested cannabinoid agonists in two muscle pain models (masseter jaw muscle and gastrocnemius calf muscle) induced by hypertonic saline injection. In the masseter model, both systemic (intraperitoneal) and local (intramuscular) administration of CB1 and CB2 agonists reduced pain behavior.

In the gastrocnemius model, local intramuscular administration was more effective than systemic administration. Selective antagonists confirmed that both CB1 and CB2 receptors contributed to the pain-reducing effects, establishing that the analgesia was genuinely mediated through cannabinoid receptors.

Why it matters

Musculoskeletal pain is extremely common and often difficult to control. Current treatments have significant limitations. The finding that cannabinoids can be injected directly into the affected muscle, avoiding systemic side effects including psychoactive effects, opens a potential new treatment approach.

The numbers in context

Three agonists tested: WIN 55,212-2 (non-selective), ACEA (CB1-selective), JWH 015 (CB2-selective). Two antagonists for verification: AM 251 (CB1), AM 630 (CB2). Two pain models: masseter and gastrocnemius. Local injection was superior to systemic in the gastrocnemius model.

How the study worked

Rat models using hypertonic saline injection to induce pain in masseter and gastrocnemius muscles. Tested non-selective agonist WIN 55,212-2, selective CB1 agonist ACEA, and selective CB2 agonist JWH 015. Verified specificity with selective antagonists AM 251 (CB1) and AM 630 (CB2).

What this study cannot tell us

This was an animal study using acute pain models that may not represent chronic musculoskeletal pain conditions in humans. The doses and administration routes may not translate directly to clinical use. Long-term effects of local cannabinoid injection were not assessed.

How to read the evidence

Animal study with appropriate controls and receptor verification; preliminary evidence for a novel administration route.

When this study was published

Published in 2012. Topical and local cannabinoid preparations for pain have since become a growing area of research and product development.

The bigger picture

Local cannabinoid administration for muscle pain could bypass many of the concerns about systemic cannabinoid use, including psychoactive effects, tolerance, and dependence. This approach aligns with the broader trend toward targeted, local pain treatments.

Questions still open

Could local cannabinoid injections treat chronic muscle pain conditions like fibromyalgia or myofascial pain? Would topical cannabinoid preparations reach sufficient muscle concentrations? How does local cannabinoid analgesia compare to local anesthetic injections?

Common questions

Why inject cannabinoids directly into the muscle?

Local injection delivers the drug directly to where the pain originates, potentially providing stronger pain relief at the site while avoiding the psychoactive and other systemic side effects that come with taking cannabinoids orally or by inhalation.

Which cannabinoid receptors are involved in muscle pain relief?

Both CB1 and CB2 receptors contributed to reducing muscle pain in this study. This was confirmed by using selective agonists for each receptor type and by showing that selective antagonists blocked the pain-relieving effects. CB2 activation is particularly interesting because it does not produce psychoactive effects.

Read the original research

Cannabinoids and muscular pain. Effectiveness of the local administration in rat.

European journal of pain (London, England), 16(8), 1116-27

View on PubMed ↗

Citation

Sánchez Robles, E Ma; Bagües Arias, A; Martín Fontelles, Ma I. (2012). Cannabinoids and muscular pain. Effectiveness of the local administration in rat.. European journal of pain (London, England), 16(8), 1116-27.