Below are the major categories of dewormers available in equine medicine. Deworming is no longer just about rotation and additionally some dewormers can be toxic given incorrectly. To develop adequate deworming protocols suitable for your horse, please consult your veterinarian.


This class of drug, also known as macrocyclic lactones, is fermented by-products of a microorganism. They function by disrupting neuro-muscular transmission of the parasite and thereby causing paralysis and death. The most commonly used macrocyclic lactones in equine medicine are ivermectin and moxidectin with the length of time before eggs begin to re-appear in the manure occurring from 8 to 12 weeks, respectively.


This category of dewormer is absorbed by the parasite and thought to interfere with its energy metabolism, intracellular structure and functions. Contact time of the drug seems to improve its efficacy and the horse’s cecum and large colon appear to prolong this time making it a useful drug. This drug is one of the safest equine dewormers with an egg reappearance time of 4-8 weeks depending on the parasite. Fenbendazole and oxibendazole are some of the more frequently used benzimidazoles.


This drug is classified as a tetrahydropyrimidine, and although fairly safe, the label recommends the product should not be used on severely debilitated horses. This drug acts as a neuromuscular blocking agent that paralyzed the parasite with approximately 4 weeks until eggs reappear in the manure. This is the drug used in Strongid-C daily deworming.


While the exact mechanism of action is unknown, it is often combined with other drugs to treat tapeworms because they have unique nervous systems that would not respond to the drugs listed above.