CBD, also knowns as cannabidiol, is a compound found in the plant Cannabis sativa, commonly referred to as marijuana. Cannabis actually produces two compounds of interest, tetra-hydro-cannabinol (THC) and cannabidiol (CBD).
THC is popular with some people for its psychoactive effects, while CBD has shown to have some therapeutic benefits. Also of note, is “hemp”, which is the same plant, but a different cultivar, which mean the same plant is bred for specific qualities. In this case, hemp is grown and used largely for its commercial or industrial use, and is bred to only have 0.3% of THC (based on the USA Federal Farm Bill Act 2018 Sect 297A, hemp must have less than 0.3% delta-9 tetrahydrocannabinol) and usually around 3% CBD, but some varieties may contain up to 25% CBD. In Canada, all cannabinoids are regulated under the Cannabis Act of 2018. Industrial hemp must have less than 0.3% THC, but there is no legal limit to the amount of CBD.
Because hemp is a fast-growing plant, it is also of interest as a potential useful product for horses, as either bedding and/or a high-fiber feed source. A byproduct of hemp is hemp seed oil, which generally only contains marginal amounts of CBD. It should be noted that hemp (or its oil) is not currently approved as a feed ingredient for horses in the US or Canada, although the Hemp Feed Coalition hopes to change that.
Cannabidiol has demonstrated numerous therapeutic benefits in people, including helping those with anxiety, multiple sclerosis, rheumatoid arthritis and others. In fact, the FDA of the United States recognizes CBD as a pharmaceutical drug for humans. In Canada, it is a controlled substance and Health Canada oversees its production and use for humans. If CBD is sold with a health claim, it needs to go through Food and Drug Regulations.
However, this becomes more complicated for its use with animals. CBD is not approved as a pharmaceutical therapy for animals, and yet it is also non-nutritional, often being called a nutraceutical. As we know, much of the nutraceutical industry is unregulated.
Despite these issues, horse owners (and other pet owners) have recognized cannabidiols as potential therapeutics for their animals. T
he administration of CBD to horses has gained popularity, despite only a handful of research studies investigating safety or efficacy in horses.
Ellis and Contino (2019) reported improvements in a horse with severe pain sensitivity when fed 500 mg CBD per day. Another study reported lower reactivity (spookability) after 6 weeks of supplementing with 100 mg of CBD daily (Draeger et al., 2021). An in vitro study ‒ conducted in a lab, not in an actual horse ‒ by Turner et al., 2021, reported decreased inflammatory cytokines (proteins associated with pain and inflammation) from cells bathed in 4 µg/ml of CBD.
Pharmacokinetics studies looking at the absorption and clearance of CBD were conducted by Williams et al., 2022. A dose of 0.35 mg/kg BW (body weight) of the horse was administered (~175 mg for a 500 kg/1100 lb horse), given orally, showed a peak in blood CBD at about two hours post-feeding and was generally cleared from the system within 12 hours. A higher dose of 2 mg/kg BW (~1000mg, or 1 g) also resulted in peak blood concentrations after about two hours, but it took up to two days to clear the system.
It should be noted that metabolites may remain in the system longer.
This study also reported no ill effects in any of the horses. However, it is important to note that despite the relatively high dose in the 2 mg/kg BW treatment, plasma concentrations only got up to about 51 ng/ml (nanograms per millilitre), well below the effective concentrations of 4 µg/ml (micrograms per millilitre) reported above by Turner (nanograms are smaller than micrograms). Therefore, a horse might need significantly higher oral doses of CBD for any effectiveness against pain and inflammation. It should also be noted that while the CBD product used in the Williams study did not report having any THC, THC was indeed detected in the blood (!).
Regardless of a clear benefit in horses, both the FEI and United States Equestrian Federation have included CBD/CBDA on the banned substances list, meaning that it is not permitted for use in the competition horse at any time. Any type of cannaboid derivative will lead to a positive test, resulting in a fine and the possibility of suspension. In Canada, CBD in equine samples will result in an infraction, with the penalty determined by the Equine Medication Control Committee.
The legal concerns even extend to those not competing, as CBD is still considered a Schedule 2 Drug in Canada and veterinarians are not allowed to prescribe these products. This puts the animal owner at the sole position of determining if CBD is the right option for their animal, and to scrutinize the source where they are getting it. It also forces owners to be responsible for any ill effects an animal may have.