Cannabis Medicinal Use
Cannabinoids and Pain Relief
Pain relief (analgesia) or decreased pain sensitivity (antinociception) are among the most commonly-cited therapeutic effects of smoking cannabis. Although cannabis products have been used for thousands of years to treat pain and other conditions, it was not until the discovery of the ‘cannabis receptor’ in the late 1980s that modern medicine started to take cannabis seriously.
The past two decades have seen an explosion of research into cannabinoid metabolism, with at least two types of receptors (CB1 in the brain and spinal cord, and CB2 in the peripheral tissues) identified, and a number of endogenous ligands (endocannabinoids), the best known of which is anandamide. Pharmaceutical research is developing apace, with discovery of a number of substances (synthetic cannabinoids) which both bind to the receptors producing an effect (agonists) and block receptors preventing any effect (antagonists), as well as enzymes which break down or modulate the activity of endocannabinoids.
Research has moved on from asking ‘whether’ – i.e. do cannabinoids produce analgesia – there is now overwhelming evidence of this, through the ‘how’ – via receptor-mediated regulation of pain thresholds in the peripheral and spinal tissues, towards the question of how to produce analgesia more effectively, and the further questions arising from these discoveries. The ‘Holy Grail’ of cannabinoid research is to develop a drug which specifically targets the pain mechanisms, but does not produce the psychotropic effects (the ‘high’) from THC. Discovery of the endocannabinoid system has revolutionised pain research, and led to greater understanding of brain and spinal function.
One of the first modern reviews of the use of cannabis as an analgesic (pain relief) agent was undertaken by Professor Rafael Mechoulam . A number of researchers using ∆9 THC injections in mice, with dosages of 5-80 mg/kg, have observed significant antinociceptive (pain relieving) activity against thermal, mechanical, electrical and chemical stimuli. In some cases the effect of cannabinoids was stronger than with opioid preparations, and other researchers noted a flat response curve (i.e. once the effective dose level is reached, further dose increases cause no additional effect). Other researchers have found cannabis to potentiate the analgesic effects of opiates . Significant analgesia has been produced in animals with injections into the brain stem and spinal cord.
The dosages required to produce detectable pain relief in animal models were substantially in excess of dosages encountered in normal social use (typically 0.1-1.0 mg/kg). The effective dose of THC in the early mouse studies (approx. 5mg/kg) would be the equivalent of an average 70kg man consuming 350mg THC, or smoking 10 grams of cannabis with a potency of 3.5%. However in most clinical trials of cannabis-extracts, dosages have generally been much lower than would be encountered in typical social use.
The following sections provide detailed reviews and citations from original scientific papers, including anecdotal evidence, animal and receptor studies, human studies including clinical trials, and learned reviews. Much of the language, particularly within quotations, is technical and intended for a specialist reader with a background in biological sciences. Non-specialist readers may wish to skip to the summary (section 6.9).