Phenobarbital is injected into injured or dying race horses in order to ease their transition into death, bringing on coma and eventually stopping the horse's heart, killing it in relatively short order. There is wide concern throughout the United States about the conditions under which race horses are raised as well as concerning the conditions under which they run races.
Race horses frequently injure themselves and their riders during practice and races. The number of horses killed and injured in accidents and euthanized subsequent to accidents has provoked extensive controversy over how horse racing is regulated and over the insufficient safety checks applied by tracks and monitoring agencies.
Many cases of horse injury and subsequent euthanasia are suspected to derive from doping, misuse of legal painkillers and other drug use. Horses already injured or suffering from illness are sometimes drugged so that they can race through their infirmity, but these horses are much more likely to suffer further injury while racing.
Euthanasia is a controversial practice but mostly because it is applied on such a broad scale due to poor management of the sport of horse racing. The practice itself is reliable and humane, painless to the horses, but some believe that it is applied far too often for comfort.