The recent damning report from the World Anti-Doping Agency's independent commission has once again put performance-enhancing drugs in the headlines.
The Straits Times consults specialist sports physician Dr Patrick Goh to break down some of these substances and doping methods and how they work to give different athletes an edge, illegally.
Prohibited at all times
What it is: A hormone that stimulates the creation of new red blood cells.
What it does: Red blood cells carry oxygen from the heart to working muscles. More such cells help increase endurance and aids recovery from training.
Who it aids: Athletes whose sport requires endurance, such as long-distance runners and cyclists. Those who do repeated sprints could also stand to benefit.
Who has been caught: American cyclist Floyd Landis
Side effects: High hematocrit levels, when the amount of red blood cells rises, causing blood to sludge, clogging capillary circulation which could lead to strokes or heart attacks.
What it is: Synthetic male hormones, or testosterone
What it does: Promotes building of muscle mass, thus increasing power and strength. Also aids recovery. Usually taken during pre-competition.
Who it aids: Throwers, weightlifters and athletes who want to build strength and power.
Who has been caught: Marion Jones, who used THG or tetrahydrogestrinone.
Side effects: Tumours, heart and fertility issues. Cosmetic side effects include balding. Women become more masculine while men may develop breast tissue.
What it is: Not a performance-enhancing drug on its own, but used to cover up the use of other drugs.
What it does: Promote urine flow, helping to flush out traces of prohibited drugs. The loss of water can also help in temporary weight loss if athletes need to make weight.
Who it aids: Athletes in sports with weight categories like weightlifting, and those who need to mask their use of prohibited drugs.
Who has been caught: Nigerian weightlifter Chika Amalaha, who was stripped of her 2014 Commonwealth Games gold for testing positive for a banned diuretic and masking agent.
Side effects: Dehydration, muscle cramps
What it is: A method used to manipulate and increase an athlete's red blood cell count, commonly done through blood transfusion.
What it does: Involves drawing out blood, storing it, and injecting the blood back into an athlete's body just before competition. Results in instant higher red blood cell count and similar effects to EPO.
Who it aids: Athletes who benefit from greater endurance and faster recovery.
Who has been caught: American cyclist Lance Armstrong
Side effects: High levels of red blood cell count, causing blood to sludge. Higher risks of blood sludging in endurance athletes as they dehydrate during a race.
Prohibited in competition
What it is: Substances that stimulate the central nervous system.
What it does: An in-competition drug that gives athletes more alertness and aggression.
Who it aids: Cyclists, throwers and athletes who need extra intensity in competition.
Who has been caught: China swimmer Sun Yang.
Side effects: Heart problems and addiction
Prohibited in certain sports
What it is: A drug that blocks the effects of adrenaline, and is commonly prescribed for conditions such as hypertension.
What it does: Has a relaxing effect and helps the heart work more efficiently, slowing heart rate
Who it aids: Athletes who benefit from a calming effect, such as shooters and archers.
Who has been caught: North Korean shooter Kim Jong Su, who was stripped of his 2008 Olympic silver and bronze medals.
Side effects: Hypotension, heart problems