Ractopamine is a drug that is used as a feed additive to promote leanness in animals raised for their meat. Pharmacologically, it is a beta-adrenoceptor agonist. It is the active ingredient in products known as Paylean for swine and Optaflexx for cattle, developed by Elanco Animal Health, a division of Eli Lilly and Company, for use in food animals for growth promotion.
The beta agonist drug ractopamine, which reduces the overall fat content of meat, is currently used in about 45 percent of US pigs, 30 percent of ration-fed cattle, and an unknown percentage of turkeys. Up to 20 percent of ractopamine remains in the meat you buy from the supermarket.
… another reason to stay away from store bought, feed lot fattened meat.