Problematic medical marijuana,but not all cannabinoids?

To the Editor

The recent letter (Chopra, 2017) correctly points out that legalisation of ‘medical marijuana’ is incompatible with good mental health promotion. The views are supported by a recent survey of use in the United States, where the drug is legalised (Hasin et al., 2017). It notes the concerning trend, that in states where marijuana is legal, illicit use and cannabis use disorders have increased more than in states where the drug is not legal. A prudent course of action would seem to argue for retention of existing prohibitive laws despite widespread use. Use in those with mental health disorders needs to be discouraged, as does heavy use in adolescents, due to an association with potential ongoing neurocognitive impairments.

The statement (Chopra, 2017) that the use of medical cannabinoids for any purpose, including research under closely observed conditions ignores known cannabinoid pharmacology and potential therapeutic value. Cannabis sativa and related species contain at least 60 different cannabinoids (Borgelt et al., 2013). The two principal neuroactive compounds are Δ9-tetrahydro-cannabinol (THC) and cannabidiol (CBD) (Devinsky et al., 2014). The basis of the plant’s psychoactive effects have been aided by the identification of central cannabinoid receptors, and the endogenous cannabinoids, anandamide and 2-arachidonoylglycerol (2-AG) (Borgelt et al., 2013). Localisation of CB1 receptors to neurons in various brain regions probably explains the physiological and cognitive effects observed with THC. CB2 receptors are located on immune cells, tissues and microglia. Binding to these receptors may explain anti-inflammatory and immunosuppressive effects. While THC binds to CB1 and CB2 receptors, CBD is inactive, which likely accounts for its lack of psychoactive properties. Nevertheless, the compound possesses affinity for a wide range of other receptors (Devinsky et al., 2014). It is these properties which make the compound of interest for therapeutic use in a diverse range of disorders. While epilepsy is perhaps the better characterised use of the compound (Devinsky et al., 2014), other conditions may potentially benefit from the use of CBD. Therapeutic benefits are not well established however and require placebo controlled trials examining dose response relationships and long-term safety data.

It can be agreed that administering CBD as part of a cocktail derived from ‘kitchen sink’ extracts of cannabis exhibits poor-quality control over doses administered. Furthermore, the THC content is also likely to vary and confound the interpretation of any outcome. Anecdotal reports of efficacy for intractable epilepsies in children demands a more serious scientific approach.