Animal models suggest that cannabinoids have potent antinociceptive effects (Fox et al. 2001). Analgesic effects are thought to be mediated by binding to cannabinoid receptors within the CNS (CB1 receptor) and in the periphery (CB2 receptor). Additionally, cannabinoids are also capable of influencing serotonergic and dopaminergic activity and endogenous opiates, thereby influencing pain transmission. Cannabinoids have been advocated for use in migraine prophylaxis and neuropathy and for anti-inflammatory purposes. For example, dronabinol (10 mg/day) was effective in reducing spontaneous pain associated with multiple sclerosis and was more effective than placebo in a small study (Svendsen et al. 2004). Side effects were common, unfortunately, and included fatigue, dizziness, headache, muscle ache, and potential mood disturbances (e.g., anxiety, mania). Several oral cannabinoids are currently under development for anti-inflammatory and neuropathic pain conditions; development of agents with specificity for the peripheral CB2 receptor may provide sufficient analgesia while avoiding untoward effects associated with central (CB1) receptor activity (e.g., fatigue, dizziness).
Table 5-15. Herbal agents used for pain
Evening primrose oil Feverfew Ginkgo biloba Goldenseal
Topical St. John's
Menstrual pain Anti-inflammatory
Anti-inflammatory; rheumatoid arthritis, migraine Anti-inflammatory; migraine Claudication-related pain Anti-inflammatory
Can produce adverse gastrointestinal (GI) effects; and abdominal, headache, and joint pain; can increase intensity of contraceptives
Acts as emetic; may interfere with anticoagulants
May trigger temporal lobe epilepsy; unsafe in patients taking phenothiazine antipsychotics
Interacts with antithrombotic agents
Can produce GI distress, headache
Can produce seizure, B vitamin deficiencies; induces abortion in pregnancy
Can potentiate sedation from barbiturates and alcohol
GI distress; can produce serotonin syndrome if combined with selective serotonin reuptake inhibitors (uncertain if this is a risk with topical applications)
GI distress, insomnia; interferes with anticonvulsants and anxiolytics
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