As far back as evidence can be gathered, humans used various plants to treat their ailments, and presumably, those of their animals. Prescriptions for the use of various plants can be found in the medical lexicon of virtually every society in recorded history. However, herbal medications lost popularity as they could no longer match the advances of science and the resulting public trust that accompanied those advances. The trend from crude plant to synthetic drug has continued, but due to the obvious fact that some herbal and botanical remedies contain pharmacologically active ingredients, the development of drugs from plants continues, and many drug companies are engaged in large-scale pharmacological screening of herbs.
Today, in laboratory settings, plant extracts have been shown to have a variety of pharmacological effects, including anti-inflammatory, vasodilatory, antimicrobial, anticonvulsant, sedative, and anti-fever effects. This should not be surprising, as many plants contain pharmacologically active ingredients, some of which are highly toxic. These sorts of substances are thought to be defense mechanisms for survival of the plant. Whether the actions of plants or extracts that have been shown to have pharmacologic effects can be safely or effectively used as medicines is another question, and one that largely has yet to be answered.
Popular herbalism (with its slogan of “botanicals are natural and safer”) appears to have abandoned most of the obvious pharmacologically active herbs (such as belladonna, ergot, and colchicum) to the pharmaceutical industry, since their therapeutic window is so narrow and misuse can be deadly. Those that remain in more common use are likely not to be either very potent or very toxic. Indeed, not only are popular herbal products not likely to be very potent or toxic, many of the products intended for use in horses contain ingredients with no recognized therapeutic value at all. That is, the products may contain a variety of plants, but the plants don’t necessarily do anything other than take up space in the package. Herbs such as burdock root, “cleavers” (derived from a climbing plant that is common in England), oregano and dandelion have no currently known or demonstrated therapeutic value, although all of them are ingredients in an over-the-counter herbal “anti-itch” preparation sold to horse owners. For such products, either there is an unknown mechanism of action, or there is a significant treatment effect on the horse owner.
Herbal medicines do present real risks of adverse effects, interactions with genuine pharmaceuticals, and positive drug tests in performance and racing horses. Allergic reactions, toxic reactions, adverse effects related to an herb’s desired pharmacological actions, and possible cancer-causing effects have been identified. Several reviews summarizing side effects and interactions have been published.
For example, nonsteroidal anti-inflammatory drugs, such as phenylbutazone or flunixin meglumine (Banamine®) have the have the potential to interact with a number of herbal supplements that are known to possess activity against blood clotting. Tea tree oil, popular in some preparations applied to the horse’s skin, can cause skin irritation and inflammation. Positive drug tests have resulted from administration of guarana to racehorses (it contains high amounts of caffeine). Given the lack of information about reactions and interactions in horses, it is almost certainly best to avoid giving drugs and herbal products at the same time.
In fact, there’s really no evidence to suggest that any herbal preparation is useful for the treatment of horses at all. If your horse needs medication, it’s best to stick to medications with proven effectiveness. But when it comes to botanical products, hay and grass are certainly important!