Equine doping --- the administration of drugs to horses --- can be traced back to Roman times. In the past, owners and trainers drugged competitors' horses to diminish their performance. Nowadays, the trend is toward stimulating a horse to victory.
Caffeine is a stimulant found in coffee, tea, and other food products. It is considered a performance-enhancing drug. Caffeine is also found in chocolate, which is sometimes offered to horses as a treat. Trainers need to be careful not to give chocolate to a horse too close to a race.
Theophylline is a bronchodilator used to treat asthma in humans by opening the airways to permit better breathing. In horses, theophylline has an effect similar to caffeine and thus is also considered a performance-enhancing drug. Both drugs enhance blood sugar and disguise fatigue.
Both caffeine and theophylline are banned from all forms of horse racing. They are also banned from use by horses participating in the Olympics. Caffeine and theophylline both can be detected by either a blood or urine test. A horse that tests positive for either substance is disqualified, and its trainer can be fined, suspended or otherwise penalised.