Medicinal Cannabis

You can’t fail to have noticed the rise of medicinal cannabis- it’s all over the news and social media. It’s a subject that causes strong feelings, so I thought we’d take a look at the current state of knowledge.

What is medicinal cannabis?

I’m going to assume you know what cannabis is- it’s a plant that contains more than 400 chemicals, of which 104 are cannabinoids – a class of chemical that acts on the cannabinoid receptor in the brain. These cannabinoids can have psychoactive effects (one such cannabinoid is THC) i.e. affect emotions, mood etc.; other cannabinoids may have useful medicinal therapeutic effects, and this is what medical professionals are primarily interested in. (one such cannaboid is cannabidiol – CBD). Cannabis is the scientific name for the species’ of plant which contains strains such as marijuana and hemp (a strain that contains less than 0.3% of THC).

Legal status

In July 2018 the UK agreed some medicinal cannaboids may be made available on prescription- however it’s important to note the difference between prescribed cannaboids and their natural relatives; the compounds available on prescriptions usually only contain one or two cannaboids, rather than the whole range which we see in the natural plant. As such, they usually have little psychoactive effect. Usually these are extracted from hemp.

THC is the cannabinoid the Government worries about- it is a psychoactive compound, is illegal, and is not found in cannabidiol (CBD oil). To reiterate: THC is not found in CBD products – CBD oil will not “drug” your pet or make them “high”

On the 14th September 2018, the Veterinary Medicines Directorate stated : “The VMD considers that veterinary products containing Cannabidiol [CBD, a substance derived from the cannabis plant] are veterinary medicines.”

Simply put, marijuana and THC containing products are illegal, hemp and CBD oil are not illegal.

Does it work?

Interestingly, the VMD is not necessarily interested in whether a medicine works or not! They are only interested in chemicals which either have a proven effect on the body, or if a manufacturer CLAIMS it has an effect on the body. So just because a medicine has a license, it doesn’t necessarily mean it has an effect! However, there are some interesting studies which show some effect, and the VMD has stated that the license was granted on this basis. i.e. the VMD thinks CBD oil works – however since it is now considered a veterinary medicine it cannot now legally be marketed or sold as a food supplement to animals and must be prescribed by a vet.

Cannabidiol (CBD oil)

Cannabidiol (CBD) is a natural product of the cannabis plant, just like THC. However CBD is believed to have the opposite effect to THC- it is non addictive and reduces the risk of seizures (fits). In fact, the earliest proponents of CBD have shown effect for reducing seizures especially in resistant forms of epilepsy.

It appears all mammals have something called endocannabinoid system – a system of cannabinoid neurotransmitters and receptors both in the central nervous system and in the peripheral nervous system. It’s important in a wide array of processes including development, fertility, pregnancy, appetite as well as cognitive processes. As such, it appears CBD oil acts on some of these receptors to produce its effects- such as seizure management. It is likely that CBD oil has other, as yet unproven, effects. However CBD oil is relatively new in medicine and we should watch this space with interest!

An initial investigation into CBD oil in epilepsy involving 30 healthy research animals found that CBD was well tolerated and resulted in measurable blood concentrations. Dr. Stephanie McGrath, a neurologist and assistant professor at Colorado State University’s College of Veterinary Medicine & Biomedical Sciences expects results of that study will be published this year. Data from the other studies are being analysed, but preliminary results of the epilepsy investigation were promising enough that in January 2018, Dr. McGrath began a three-year crossover study of CBD for epilepsy in dogs with a $350,000 grant from the American Kennel Club.

Other claims have been made for CBD namely pain relief, modulating immune response, treating cancer and for reducing anxiety. Evidence is still weak for these claims though. This lack of evidence means vets are reluctant to back its use for these conditions.


The lack of evidence along with the rise in positive coverage of medicinal cannabis has meant the rise in owners self medicating their pets. Unfortunately marijuana can be toxic to animals, and a paper in 2012 by the Journal of Veterinary Emergency and Critical Care found the number of cases of poisoning by cannabis quadrupled in the 5 years after legalisation of its use in Colorado. Potential adverse effects of poisoning by marijuana include seizures, agitation, and pneumonia. Luckily the fatal dose is high, but adverse signs can start at quite low levels. It’s important to realise that CBD oil has very low toxicity and can generally be used quite safely.