What is Cannabidiol?
Cannabidiol (CBD) is one of many substances (collectively called cannabinoids) that occur naturally in the plant species Cannabis sativa. Cannabis has traditionally been used by humans for its psychoactive effects, which are mainly due to the cannabinoid delta-9-tetrahydrocannabinol (THC). Cannabis used in this way is also known as marijuana. Industrial hemp is a strain of cannabis or products of the cannabis plant (e.g. grown for fibre or seed) that contain low levels of THC. There is a now a lot of interest in studying the effects of cannabinoids, particularly CBD, in the management of pain in humans and dogs.
How does CBD work?
Mammals produce substances (which have become known as endocannabinoids) that interact with the same receptors in the body as cannabinoids. This has led to the notion that humans and dogs have an endocannabinoid system. However, the exact role of endocannabinoids in the body is not yet clear. They appear to be involved in various bodily functions, including the control of appetite, mood and pain perception. So far the precise mode of action that CBD might have in relieving pain is not understood, but more information is emerging from research.
What is the legal status of CBD products for animals in the UK?
In the UK, CBD is considered to be a veterinary medicine. The veterinary medicines regulator (the Veterinary Medicines Directorate [VMD]) made this clear on 14 September 2018 and has since written to UK CBD suppliers and manufacturers informing them of the position (Vet Record 6 October 2018).
What does this mean?
This means that without a marketing authorisation it is illegal to sell, supply or advertise CBD products for pets, with or without specific treatment claims. There are currently no authorised CBD products for animals in the UK.
Can vets just prescribe human CBD?
A vet may prescribe a human medicine for a pet in accordance with the veterinary prescribing cascade, which allows the clinical needs of an animal to be met with an unlicensed product. Products containing CBD that are marketed for medical purposes are considered by the human medicines regulator (the MHRA) to be medicines, and so require a marketing authorisation. There are currently no products containing CBD alone authorised in the UK for medical use in humans.
Some companies market human CBD products as supplements. It is illegal to make specific medical claims for these without a marketing authorisation. These products are unregulated and not standardised and so we cannot be sure what they contain.
What is the clinical evidence on CBD in dogs with OA?
So far, only one clinical trial (of an industrial hemp extract containing ~10mg/mL CBD and small amounts of THC) has been published in full (Gamble et al 2018). The trial has several limitations: a small number of dogs, the lack of an objective measurement of effect, a relatively short duration for a chronic condition with signs that wax and wane, and it was funded by the company that markets the extract used in the study. Other studies are ongoing but it is too soon to know whether CBD is effective at relieving pain in dogs.
What is the safety of CBD in dogs?
If it is effective in dogs, we don’t yet know the optimum dose and we know very little about the side effects, except that in the small published clinical trial liver enzymes were raised in more than half of the dogs while on CBD. In humans, CBD is metabolised by liver enzymes and so there is a potential for drug interactions, but whether the same applies to dogs is not known.
What is the conclusion on whether we can use CBD to treat OA pain in dogs?
All in all, there are currently too many uncertainties about whether CBD is beneficial for dogs with osteoarthritis, and no suitable products.