By Tom Fordyce

Olympic president Jacques Rogge has warned that there could be more positive dope tests in Athens than at any other Games in history.

Record numbers of athletes will be tested, new tests developed and samples frozen so they can be analysed retrospectively.

But what are the drugs and methods that cheats might be using, what benefits would they gain and how easy are they to detect?

What are they?
Substances that act on the brain to stimulate the body mentally and physically.

Athens will see more dope tests than any previous Olympics

Examples include:
Amphetamines, ephedrine, cocaine, ecstasy, salbutamol.

Why would sportsmen take them?
Allows you to compete at maximal levels for longer, reduces feelings of tiredness. Can aid weight loss.

Side effects can include:
Increased blood pressure, aggression and anxiety, addiction, loss of appetite, increased and irregular heart beat, chest pains, headaches and palpitations.

Chances of being caught:
High, if tested soon after ingestion.

What are they?
The strongest form of painkillers.

Examples include:
Morphine, methadone, heroin, pethidine.

Why would sportsmen take them?
Increases pain threshold so you can compete and train for longer and harder. Reduces or eliminates pain so can you compete despite injury or illness.

Side effects can include:
Highly addictive. Can cause loss of concentration, balance and co-ordination, drowsiness, nausea and vomiting, constipation, fainting and comas.

Chances of being caught:
If tested within three months of taking them, high.

What are they?
Natural or man-made compounds that act like the hormone testosterone.

Examples include:
Nandrolone, tetrahydrogestrinone (THG), stanozolol, androstenedione, DHEA.

Why would sportsmen take them?
Can increase muscle size, strength and power; increase aggression and competitiveness; allows you to train harder and for longer.

Side effects can include:
In males: kidney damage, development of breasts, premature baldness, shrinking and hardening of testicles, sterility and impotence, acne, increased aggression and sexual appetite.
In women: development of male features, including facial hair; deepening of the voice, irregular periods, increased aggression.

Chances of being caught:
Steroids stay in body for up to six months and are easily detectable in urine, so if tested, a user should be caught.

What are they?
Products that help eliminate fluid from the body.

Examples include:
Acetazolamide, chlorthalidone, triamterene.

Why would sportsmen take them?
To lose weight quickly in sports that have weight categories, and to disguise the presence of other banned substances by increasing the rate at which urine is produced and expelled.

Side effects can include:
Dehydration, dizziness, cramps, headaches, nausea, kidney damage.

Chances of being caught:
If tested, high - easily detectable.

What are they?
Substances produced by the body to control specific functions like growth, red blood cell production and sense of pain. Analogues are the artificial version.

Examples include:
Human growth hormone (HGH), erythropoietin (EPO), corticotrophin, human chorionic gonadotrophin (HCG).

Why would sportsmen take them?
To increase muscle size and strength (HGH, HCG), to help repair body tissue to allow quicker recovery from injury and training (HGH) and to improve blood's ability to carry oxygen and thus the athlete's ability to train and perform harder for longer (EPO).

Side effects:
Excess HGH can cause acromegaly (abnormal growth of hands, feet, face and internal organs). Misuse of EPO can cause thickening of the blood, leading to strokes, heart attacks and death.

Chances of being caught:
There is now a test for EPO, but it has caught relatively