Many cultures have used cannabis as a medicine, but prohibition agendas have hampered efforts to conduct research into the potential therapeutic effects of the drug. (Lucy Nicholson, Reuters)

It's high time we make cannabis available for medical research

Medical regulatory bodies must be guided by solid evidence rather than pressure from recreational users pushing for the legalisation of the drug.

African medical regulatory authorities such as the South African Medicines Control Council should consider applications for the approval of medicinal cannabis for the treatment of chronic pain. This is especially needed in the case of patients who are not responding well to conventional medications and in which the use of medicinal cannabis may have a positive impact on its own or as an adjunct to existing medications.

But regulatory bodies in Africa must be guided by good evidence rather than by anecdotal reports or pressure from recreational users promoting a legalisation agenda.

Policy-makers on the continent, and particularly in South Africa, need not be passive consumers of the findings of research on medicinal cannabis conducted in Europe and the United States. Instead our researchers should conduct research into the medicinal effects of cannabis in areas in which the quality of the science to date is poor or in which more research needs to be undertaken.

South Africa's Medical Research Council is well-positioned to take a leading role in the country as a conduit for local and international funding of, and support for, clinical trials of medicinal cannabis as well as other research on medicinal cannabis.

Prohibition agendas
Through the ages, many cultures have used cannabis as a medicine, but in the past 60 years prohibition agendas have hampered efforts to conduct research into the potential therapeutic effects of the drug.

Cannabis is the generic term for drugs produced from the plant, Cannabis sativa. The principal active ingredient of cannabis is the cannabinoid tetrahydrocannabinol (THC). Chemicals derived directly from the cannabis plant or those manufactured synthetically in pill form, such as nabilone and dronabinol, are known as cannabinoids. Cannabidiol (CBD), another cannabinoid, is not psychoactive but is thought to have anti-anxiety and anti-psychotic effects.

The therapeutic effects of cannabis depend on the concentration of THC and the ratio of THC to CBD. Cannabinoids can be ingested orally, placed under the tongue, absorbed through the skin in patches or balms, smoked, inhaled, used as a suppository or drunk as a herbal tea.

Absorption through oral use is slow and unpredictable, and smoking does not deliver accurate dosage. Like cigarette smoking, it also has harmful side effects associated with toxic compounds created in the combustion process. There is interest in using vaporizers as a delivery mechanism, but these can be expensive.

Positive effects
In 2013, South Africa's National Cannabis Working Group, a local lobby group seeking the legalisation of marijuana, presented a position paper to the South African Central Drug Authority highlighting various studies (mainly involving preclinical research, but some involving human participants) that pointed to positive effects of cannabis for conditions including Alzheimer's disease, amyotrophic lateral sclerosis, chronic pain, multiple sclerosis, diabetes mellitus, dystonia, fibromyalgia, incontinence, gastrointestinal disorders and various cancers, including lung cancer.

Research into medicinal cannabis has increased substantially over the past decade, particularly in North America and Europe, but hardly at all in sub-Saharan Africa. This is also true for South Africa, despite good conditions for growing high-quality cannabis outdoors.

In January 2016, South Africa's Medical Research Council released a policy brief on cannabinoids for medical use, in which we appraised a systematic review evaluating the medicinal use of cannabis, first published by Dr Penny Whiting and colleagues in the Journal of the American Medical Association in June 2015.

The systematic review was commissioned by the Swiss federal office of public health and focused on randomised controlled studies evaluating cannabinoids for the management of 10 conditions, including nausea and vomiting because of chemotherapy, chronic pain, appetite stimulation in HIV and Aids, spasticity as a result of multiple sclerosis or paraplegia, and glaucoma.

The authors identified 79 eligible randomised controlled studies – the gold-standard study design for evaluating the efficacy of interventions – after screening 23 754 publication records and assessing 505 full reports.

Trustworthy results
Our appraisal involved assessing the quality of the systematic review, focusing on the five common conditions listed above using the risk of bias for systematic reviews quality appraisal tool. We concluded that the review results were robust and trustworthy.

The review authors found evidence of a moderate quality to support the use of cannabinoids for the treatment of chronic pain and to reduce spasticity in multiple sclerosis patients, but the clinical significance of the latter remains unclear. Evidence for a beneficial effect of cannabinoids in nausea and vomiting because of chemotherapy was low, and similarly for weight gain in HIV infection. Safety concerns were raised through a number of short-term adverse events reported in persons using cannabinoids and the lack of long-term data from rigorous studies was also noted.

Increasing research on the medicinal use of cannabis to address these gaps in the current evidence base will require making medical-grade cannabis available for research in various forms and encouraging governments and international agencies to fund both preclinical research, that is cellular level and animal studies, and human trials. Trials of not only palliative care but also of treatment, for example into the possible anti-cancer effects of cannabinoids on tumour growth, will be required.

Safe supply and regulation
But support for research into medicinal cannabis must not be contrasted with a prohibition agenda against recreational use. Society has not forgone the use of morphine for fear of the recreational use of heroin. In fact, a study from the US published in 2015 in the Journal of Policy Analysis and Management suggests that medicinal cannabis policies reduce recreational cannabis consumption except in states that permit dispensaries or home cultivation.

Before medicinal cannabis can be made more widely available, even for conditions such as chronic pain in which the evidence of benefit is strongest, policy-makers will need to consider issues such as the safe supply and regulation of medicinal cannabis, the best routes for administration (including issues of dosage), cost-effectiveness and, at a later stage, issues such as the development of criteria for selecting patients who are eligible for medicinal cannabis. Methods for training doctors, pharmacists and others in prescribing and administering medicinal cannabis and for instructing patients in its use will also need to be developed.

Professor Charles Parry is the director of the alcohol, tobacco and other drug research unit at the Medical Research Council. Professors Bronwyn Myers and Nandi Siegfried are chief specialist scientists in the same unit.

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