this happens, the logical result is that additional injury can occur, rapidly accelerating the need for ever more powerful drugs to keep a horse racing. Official state testing reports do not, however, confirm that such use is widespread in post race samples, although it does occur. Federal laws allowing great latitude for veterinarians to use medications pose a concern for racing regulators who believe improper or over use puts racehorses at greater risk of crippling injuries and death. Jockeys are also exposed to far greater risk, as medicated horses are much more likely to suffer catastrophic breakdowns during a race sending horses and riders tumbling. In a series of articles on drugs and racing The New York Times estimates that approximately 24 horses are killed as a result of injuries incurred during a race each week in America, though the question of how many of these deaths are linked to misuse of medication is undetermined. For decades, outside scrutiny had been focused on the question of whether horse trainers seek increasing access to pre-race drugs to keep sore horses in training and racing. But in recent years the focus has broadened to include attending veterinarians for racehorses. Experts contend that veterinarians who provide drugs to keep injured horses racing violate veterinary practice laws regarding proper ethics, standards and practices. The issue of legal and illegal drug use in horse racing is again under review by the U.S. Congress with legislation pending before the House of Representatives and the Senate to create uniform pre-race drug rules and penalties applying in all racing states. The Interstate Horse Racing Improvement Act is endorsed by some of the most prominent names in the thoroughbred racing industry although groups representing other equine breeds, veterinarians, horsemen, and regulators have serious concerns. Performance-modifying substances Identification of these substances in a horse is viewed with great regulatory concern. Testing for these substances usually proceeds at the highest level of sensitivity possible, so-called "zero-tolerance" testing. About 1100 or so substances are classified by the Association of Racing Commissioners International (ARCI) Uniform Classification System for Foreign Substances as potentially performance-enhancing in a five-class system. The most complete listing of such substances is found online. StimulantsAmong the equine stimulants are amphetamines, as well as the amphetamine-like drugs such as methylphenidate (Ritalin). TranquilizersHorses can also be medicated to win by relaxing them, and allowing the horse to run its best possible race