Growing interest but limited evidence on the usefulness of cannabidiol in treating ophthalmic disease in dogs: a review.

The 2 most known cannabinoids are Δ9-tetrahydrocannabidiol (THC) and cannabidiol (CBD). Both chemicals are extracted from the cannabis plant but can also be synthetically produced. Δ9-Tetrahydrocannabidiol is extracted from the subspecies of the cannabis plant known as the marijuana plant, which contains a high concentration of THC (0.3% to 30%). Δ9-Tetrahydrocannabidiol is a major psychoactive and intoxicating component of the cannabis plant and is not recommended for use in dogs due to its toxic effect. Cannabidiol is extracted from the subspecies of the cannabis plant known as the hemp plant and must contain less than 0.3% THC. Cannabidiol is a major nonpsychoactive component of the cannabis plant, and its effect has been investigated for epilepsy, neoplasia, and osteoarthritis in dogs. Public interest in the medical use of cannabinoids for various diseases and disorders has grown in the last couple of years. The attention has extended to veterinary medicine, where veterinarians and pet owners are curious about what diseases the nontoxic CBD can be used for to treat companion animals. The use of CBD for ophthalmic diseases has also been investigated due to its anti-inflammatory and neuroprotective effects. Intraocular pressure regulation for glaucoma, corneal diseases (eg, keratitis and corneal pain), uveal diseases (eg, endotoxin-induced uveitis), and retinal/optic nerve head diseases (eg, diabetic retinopathy) are areas where CBD's effect has been investigated in humans and animals. The aim of this review is to give an update on what is known regarding the use of cannabinoids, especially CBD, for ophthalmic diseases in dogs.