The United States Equine Federation has announced that beginning September 1, 2019, horses competing under USEF rules who test positive for natural cannabinoids, synthetic cannabinoids, and other cannabimimetics will be considered in violation of GR4. Both USEF and FEI list natural cannabinoids, synthetic cannabinoids, and other cannabimimetics as prohibited substances. Read the full announcement here.

In addition, any human athlete who is subject to testing under the World Anti-Doping Code can refer to the regulations for human use of cannabinoids here.