1. Anabolic agents
Examples: Anabolic steroids and nandrolone
What they do: Increase muscle mass.
Side effects: When taken by men, they will initially have an increase in libido, but may subsequently become impotent. They may start to grow breast tissue or have acne. Getting angry and having liver problems are other potential side effects.
When taken by women, they become like men: Their voice deepens, they may grow beards and experience male pattern baldness.
Give an unfair advantage in: Bodybuilding, weightlifting, swimming and sprinting.
2. Hormones
Example: Erythropoietin, more commonly known as EPO.
What they do: Induce red blood cell production, which improves the amount of oxygen the blood can carry to the body's muscles. This gives athletes the ability to train and perform harder for longer.
Side effects: While there are no obvious external signs of usage, EPO consumption can lead to heart problems.
Give an unfair advantage in: Cycling, long-distance running and cross-country skiing.
3. Stimulants
Example: Amphetamine
What they do: Increase alertness and concentration. Also reduces the feeling of fatigue.
Side effects: Increased heart rate and blood pressure.
Give an unfair advantage in: Cycling, baseball.
4. Beta-blockers (banned only in some sports)
Example: Propranolol
What they do: Slow down one's heart rate, thus making one steadier.
Side effects: Fatigue, dizziness and nausea.
Give an unfair advantage in: Shooting, archery and bowling.
5. Beta-2 agonists
Example: Clenbuterol
What they do: Open up airways. They also have anabolic effects.
Side effects: Increased heart rate and tremors.
Give an unfair advantage in: Athletics.