See article Marijuana: If It’s Legal, Should You Give It to Your Pet?
Marijuana and hemp are different products from the same plant (Cannabis sativa). Marijuana is derived from the flowering buds, leaves, and resin, while hemp comes from plant stalks and sterilized seeds. Hemp products include both fiber and oils. The marijuana producing parts tend to have significantly higher concentrations of THC, the psychotropic component of Cannabis. From a regulatory perspective, a product can only be labeled as hemp if it contains less than 0.3% THC. All of the current, widely marketed veterinary products are derived from hemp. The DEA considers all Cannabis based products to contain some level of THC, and therefore, does not sanction the use of any hemp product that enters the body. Hemp containing fabric, shampoos, lotions, and other topical products that are not intended for ingestion are allowed.