Stimulants
Stimulants are generally used to help athletes stay alert, reduce fatigue and maintain aggressiveness. They act on the body to make the heart beat faster, the lungs breathe faster and the brain work faster. Stimulants include caffeine, amphetamines, ephedrine, phenylephrine, phenylproanolamine, strychnine and cocaine. Possible side effects include nervousness, shaking, irregular heartbeats, high blood pressure, convulsions and even sudden death.

Relaxants
Relaxants come in various forms, including alcohol, prescriptions such as beta-blockers, and cannabinoids such as marijuana.

Alcohol is commonly used to help people relax because it reduces activity in the brain and nervous system. While it may help an athlete relax and cope with the pressures of competition, it can also significantly impair mental functions (judgement, balance, coordination). It is restricted in the Olympics and banned altogether in certain events.

Beta-blockers are commonly prescribed to treat high blood pressure by causing the heart to slow down and blood vessels to relax. Athletes who require steady hands in competition, such as those competing in archery or shooting events, may use them. Possible side effects include lower than normal blood pressure (hypotension), slow heart rate and fatigue.

Cannabinoids, mainly marijuana and hashish, have no clinical value, but have recently been used for relieving pain in terminally ill cancer patients. Cannabinoids cause hallucinations, induce drowsiness, increase the heart rate and impair mental functions (judgment, balance, coordination and memory).
Weight Control
Diuretics are commonly prescribed to treat high blood pressure and are often found in diet pills. Diuretics act on the kidney to increase the flow of urine. Diuretics include furosemide, acetazolamide, bumetanide and ethacrynic acid. They are used by athletes whose events have weight restrictions (weightlifting, rowing, horse racing). Diuretics are also used to mask the use of other drugs. Because they increase the amount of urine produced, they dilute the concentration of other drugs in the urine. Possible side effects include dehydration, dizziness, cramps, heart damage and kidney failure.