Omeprazole is best known to people as the brand name drugs Prilosec or Nexium. It is used in horses to treat gastric ulcers. For horses, it is sold under the brand names Gastroguard, UlcerGuard and as generic omeprazole.
Omeprazole is a type of drug called a protein pump inhibitor. In horses, it turns off some of the stomach's ability to produce digestive hydrochloric acid. This gives the stomach time to heal from an ulcer.
Omeprazole is the only drug approved for use specifically for gastric ulcers in horses by the Food and Drug Administration, or FDA. It is the preferred protein pump inhibitor for horses, according to Michael J. Murray, DVM and professor at the Marion DuPont Scott Medical Center.
Omeprazole pills or paste can also be given for gastric ulcer prevention as well as for treatment. Half of the normal dose is given. Stressful situations like competitions can cause a horse's stomach to produce more acid.