Cannabinoids for pain and nausea
Some evidence but is there any need?
This is an exciting time for cannabinoid research. The discovery of cannabinoid CB1 receptors (expressed by central and peripheral neurones)1 and CB2 receptors (expressed mainly by immune cells)2 and endogenous agonists3 for these receptors has renewed the scientific community's interest. Independently of these developments society at large has continued an aggressive debate about the therapeutic use of cannabinoids, including demands for their more liberal availability. 4 5 Cannabinoids have been suggested to have therapeutic value as analgesics and in various conditions, including migraine headaches, nausea and vomiting, wasting syndrome and appetite stimulation in HIV-infected patients, muscle spasticity due to multiple sclerosis or spinal cord injury, movement disorders such as Parkinson's disease, epilepsy, and glaucoma.6 When new therapeutic indications are suggested, two major factors should be taken into account: what are the adverse effects of the treatment and how does its effectiveness compare with that of existing alternatives?
In this week's issue two high quality systematic reviews shed light on the therapeutic potential of cannabinoids in the management of pain (p 13)7 and the nausea and vomiting induced by chemotherapy (p 16).8 Campbell et al sought and examined all randomised controlled trials that compared the efficacy and safety of cannabinoids with those of conventional anaglesics.7 The nine trials included 222 patients, of whom 128 had cancer (five studies), two chronic non-malignant pain (two studies, one patient per trial), and the rest postoperative pain. Cannabinoids were no more effective than codeine in controlling acute and chronic pain and they had undesirable effects in depressing the central nervous system. These studies are mostly from the 1970s. Since then we have learnt to use non-steroidal anti-inflammatory analgesics alone and in combination with opioids in both cancer related and postoperative pain. There is thus no need for cannabinoids for these indications.