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Medical use of cannabinoids and marijuana

Evidence-based medicine

Gerry Morrow

Tuesday, 17 December 2019

AdobeStock_92196462.jpegBiologically, the cannabis plant can be known as hemp or marijuana.

Hemp is an organic source of chemical cannabidiol (CBD), which acts on brain endocannabinoid neuroreceptors as an antagonist and is therefore not psychoactive.

Marijuana contains both CBD and tetra-hydrocannabinol (THC), an endocannabinoid agonist and psychoactive. Synthetic cannabinoids are also psychoactive substances, particularly lipophilic and full agonists of the endocannabinoid neuroreceptors with no CBD.

For years, advocates of cannabis have been searching for a disease to which it can be used as a therapy.

CBD has been proposed as a treatment many diseases however the evidence does not stack up with the exception of intractable chemotherapy induced nausea and vomiting, and muscle spasticity in people with multiple sclerosis.1

The European Medicines Agency (EMA) also recently approved and licensed a CBD medication called Epidyolex for use in two rare forms of epilepsy, affecting up to 10,000 people in the UK.

Due to concerns about a lack of longer follow-up, clinically implausible extrapolations of some of the evidence and the validity of the manufacturers economic model, NICE has subsequently rejected the use of cannabidiol in these groups.3 However, the appraisal committee accepted that there was approximately a 27% reduction of drop seizures in patients with these rare forms of epilepsy, treated with a combination of clonazepam and Epidyolex.

The prescription license will therefore be restricted to this narrow cohort of patients, as a final option when other medications have failed, and its use limited to the field of neurology.

Despite this lack of evidence, the outlandish claims of vendors continue, and CBD now comes in a variety of concentrations, purity, finding its way into mainstream health food shops, high street outlets and online.

By comparison, the evidence for the clinical benefits of marijuana and THC has been even less compelling. This combined with a number of adverse effects including tolerance, nausea, anxiety, tachycardia, interference with cognitive development in children, and increased risk of schizoaffective disorders (which persists for over a year after cessation of THC intake) has not made for happy reading for the medical cannabis lobby.4

As humans, we are susceptible to the placebo effect and we are especially vulnerable to seeking therapy for conditions considered untreatable.

However, our enthusiasm needs to be tempered with likely false hope and disappointment that this can bring, especially if the drug in question comes at a great cost either financially, personally or both. The risk of deception in an unregulated market is also significant.

The reality is that CBD extracted accurately in a medicinal format can provide a benefit for a very small group of people with intractable epileptic seizures with limited risk of adverse effects. On the other hand, despite the anecdotal stories, it is difficult to label Marijuana as anything other than harmful.

Any other narrative presented to the public is based on bias, an agenda of commercial gain or a view of the world that’s skewed to be cannabis centric.


  1. NHS England. Support for Prescribers Cannabis-based products for medicinal use
  2. European Medicines Agency. EU/3/17/1855
  3. Dijk S, Lok P. NICE rejects cannabidiol for two types of treatment resistant epilepsy in children. BMJ 2019; 366 :l5280.
  4. Lafaye G, et al. Cannabis, cannabinoids, and health. Dialogues Clin Neurosci. 2017 Sep; 19(3): 309–316. PMCID: PMC5741114 PMID: 29302228

Author's Image

Gerry Morrow

With a keen interest in evidence-based medicine and patient involvement, Gerry has over twenty years’ experience working as a GP, based initially in Worcester and then in the rural practice of Allendale. Now Medical Director of Clarity Informatics, a leading IT healthcare solutions provider, Gerry is leading a globally recognised team of clinicians and researchers, and is also directly responsible for the production and delivering of Clarity’s clinical guidance which forms the clinical content of NICE’s Clinical Knowledge Summaries (CKS) service. Gerry is also a clinical non-executive director of the North East Ambulance Service, responsible for operating patient transport and ambulance response services across a region covering 3,200 square miles and a population of 2.7 million people.
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