Athletics has become a multi-billion-dollar industry - so much so, that the desire to win can drive athletes to use drugs to enhance their performance. But Marlene Klein, head of the medical department at Germany's National Anti-Doping Agency (NADA), said doping is hardly a new phenomenon.

Klein told DW that doping likely goes back to athletes in ancient Greece looking to get an edge against their competitors - and it continues today for some of the same reasons.

"Athletes have only a limited period in which they can have success," she said. "They might be tempted by media coverage, and they might be tempted by the money that comes with winning."

Medical and legal threshold

But what actually constitutes the threshold for artificial enhancement? Klein explained that two aspects define this: the legality of a drug, and the strength of its active ingredient.

"For an ill person, such substances were originally meant to heal and cure. What athletes do - what we call 'doping' - is the abuse of those substances," Klein said. Over-the-counter painkillers like ibuprofen are not only legal, but they have much less of an effect than a narcotic painkiller like morphine - which is heavily regulated.

So-called non-specified substances, on the other hand, are not available over-the-counter. Patients need a prescription from a doctor to take them - or put in some "criminal energy" to get the drugs, Klein said, adding that, "You don't fall accidentally into a syringe with EPO."

EPO stands for erythropoietin, which is a kind of peptide hormone. Doping drugs fall into five major categories. Here's a breakdown.

Steroids

Steroids, or anabolics, are naturally found in the body - like testosterone, for example. But athletes sometimes inject themselves with extra steroids to get a certain effect. "Male humans need testosterone to develop their maleness. It also stimulates muscular tissue - and that's what athletes want more of," Klein explained.

But misuse of steroids can have some serious - and seriously unpleasant - side effects. "Men can develop breasts like ladies, and some very prominent male organs may even shrink," Klein said. Anabolics also have long-term, detrimental effects on the cardiovascular system, and can damage the circulatory system.

Stanozolol, nandrolone and norandrosterone are some names for the specific steroids athletes use.

Stimulants

Stimulants put an athlete's nervous system into high gear, boosting alertness and masking fatigue. They're banned during actual competition, but "athletes use them before competition to have extra energy," Klein said.

After the effects have worn off, the athlete could feel extreme exhaustion. Abuse of stimulants can strain the cardiovascular system, and even cause heart failure.

Argentine soccer legend Diego Maradona tested positive for using the stimulant ephedrine at the soccer World Cup in 1994.

Hormones and peptide hormones

Hormones, like steroids, also occur naturally in the body, but can be injected for added effect. Insulin, for example, plays a life-saving role for diabetics. But "in a healthy person, insulin may have the effect that you lose fat - which sounds nice - and that you build up muscular tissue, which also sounds nice to an athlete," Klein said.

But taking too much might cause hypoglycemia, or dangerously low blood sugar, which keeps the body from working properly. And there's a greater danger with athletes injecting hormones: hormones work together in a delicate balance, and since hormones act as messengers telling the body what to do, any disturbance in one hormone level can affect the entire hormonal system and all bodily functions.

Peptide hormones are hormones with a specific protein structure. The most common is EPO, or erythropoietin - that's what cyclist Lance Armstrong this past January admitted to using.

Peptide hormones "stimulate the growth of red blood cells, which transport oxygen - so for an endurance athlete, this is quite helpful," Klein explained. But taking too much can overload the blood with red cells, making it thicker. The heart might not be able to pump this thick blood anymore - or the athlete could develop a deadly blood clot.

Narcotics

Narcotic analgesics, or painkillers like morphine, are major doping drugs as well. "Athletes might be tempted to take them to prevent the pain they might feel during competition, like in combat sports," Klein explained.

"Side effects can be restlessness, or you may feel drowsy, and long-term abuse can also have a long-term effect. One might have intense headaches, or nausea," Klein said. There's also the risk of addiction. And since pain acts as a warning system to prevent injuries, athletes who dope with narcotics put themselves at risk of greater injury.

Diuretics

Diuretics cause the body to expel water - important for an athlete to make it into a lower weight category in sports like wrestling, or to mask the use of other doping drugs.

Diuretics were originally used to treat high blood pressure, Klein said, "because you lose water, you dehydrate, and the pressure goes down." Their effect is short-term, but can be extreme. An overdose of diuretics can cause you to lose so much water that your circulatory system no longer functions properly. "You might lose consciousness, and it can lead to circulatory collapse," Klein said.

Doping's future

Groups like the World Anti-Doping Agency and its German counterpart NADA work on education for prevention of doping abuses. They also coordinate with the pharmaceutical industry to develop new means of detection, and with law enforcement to monitor the black market.

Klein said "the net is actually getting tighter, and it's more difficult for athletes to cheat." Given all the potential negative effects of doping, this might be a good thing.