The best evidence we have to date is that medicinal cannabis is ineffective for nociceptive pain arising from tissue injury or arthritis. It may have some benefit for certain subtypes of neuropathic pain, such as the pain of multiple sclerosis [1], although more work needs to be done to clarify this.
A recent review by the Cochrane Systemic Review Committee in which 16 studies were evaluated showed that the number needed to treat for benefit is 11 – this means that 11 patients would have to be treated with medicinal cannabis for just 1 patient to achieve a reduction in their neuropathic pain by 30%, with the other 10 not deriving that stated benefit [2]. The review also showed that for every 10 patients treated with cannabis based medicines, 1 patient would develop a psychiatric disorder. This suggests that there is an incidence of harm with medicinal cannabis that is equal to the chance of modest clinical benefit with medicinal cannabis for neuropathic pain. This obviously mandates that safer types of medicinal cannabis be developed and that further work needs to be done on subtypes of neuropathic pain patients to determine those that may properly benefit from it.
The Faculty of Pain Medicine (ANZCA) have put forth a statement on medicinal cannabis, with particular reference to its use in the management of patients with chronic non-cancer pain: http://fpm.anzca.edu.au/documents/pm10-2018.pdf
A cannabis prescription advisory service has been set up by the New South Wales Department of Health and is based at John Hunter Hospital. The phone number for this service is 02 4923 6200.