Are Performance-Enhancing Drugs Prohibited in Islam?
Question

What is the ruling on buying and selling, and taking, performance-enhancing drugs in sports? Some people told me that they are not prohibited because they are not (street) drugs, and so long as they do not cause harm there is nothing wrong with taking them either. In fact a doctor told me: There is nothing wrong with taking them, because they do not cause any harm to the body, so long as the dose is no greater than 20 ml. What is the Islamic view on that?
Praise be to Allah.Harm caused by performance-enhancing drugs in sports
Performance-enhancing drugs are banned in the world of sports; that includes using any substance that could enhance the performance of any athlete in an abnormal manner and give him an unfair advantage in competition.
The phrase ‘performance-enhancing drugs’ includes both manufactured medicines and natural substances that may be taken in unusual quantities or in the usual manner that may contribute to an abnormal rise in physical agility. However in most cases, these drugs are like other (harmful) drugs.
Types of Performance-Enhancing Drugs Banned in Athletics
The Medical Commission of the International Olympic Committee has divided banned performance-enhancing drugs used in sports into a number of categories, as follows:

Stimulants affecting the nervous system
Depressants affecting the nervous system
Metabolic hormones
Vasoactive drugs (affecting the circulatory system)
Diuretics
Growth hormone
Cortisone

Medical Risks Associated with Performance-Enhancing Drugs
Medical research has proven that taking performance-enhancing drugs leads to psychological illnesses such as mood swings, depression, aggressiveness, mental illness and insanity.
It also leads to physical illnesses such as heart attack that may cause death, kidney disease, tumours in the prostate, impotence leading to sterility, and hormonal imbalance.
It is possible to clarify the physical harm that is confirmed by medical research, which proves that taking performance-enhancing drugs causes the following:

Addiction
Depression
Hepatitis
Gastritis leading to stomach ulcers
Various mental illnesses
Insomnia and hallucinations
Diarrhoea and nausea
Balance disorders
Lung and heart disease
Loss of appetite
Muscular atrophy
Increased production of tears and nasal mucus
Skin rashes
Slowed breathing rate leading to death
Kidney disease
Tumours in the prostate
Development of male physical characteristics in females
Impotence or sterility as a result of using testosterone (male hormone)

Islamic Rulings on taking performance-enhancing drugs
It is possible to find out the ruling on taking performance-enhancing drugs by noting the physical harm that they cause to the athlete himself.
It is clear from the above list of illnesses that stem from taking performance-enhancing drugs, and from what specialists have said about the extent of harm that result from taking these drugs, in either the short term or the long term, that using performance-enhancing drugs is not permissible, because of what it leads to of harm that may cause death. Allah, may He be Exalted, says (interpretation of the meaning):
{And do not kill yourselves (nor kill one another). Surely, Allah is Most Merciful to you.} [An-Nisa 4:29]
{and do not throw yourselves into destruction.} [Al-Baqarah 2:195]
And the Messenger of Allah (blessings and peace of Allah be upon him) said: “There should be neither harm nor reciprocating of harm.” (Narrated by Ibn Majah with a sound chain of narration)
Islam forbids the Muslim to cause his own death or kill himself; it also forbids him to harm himself in any manner.
Source:
Adapted from a Master’s thesis entitled An-Nawazil fil-Ashribah (New issues concerning drinks), p. 229-234, by Shaykh Zayn Al-`Abidin, son of Shaykh Ibn Azwin, supervised by Shaykh Sa`d ibn Turki Al-Khathlan
For more details, please see the following answers:
Aphrodisiacs and the ruling on taking them
Ruling on consuming hemp protein
Using medicine to increase growth hormone and treat short stature
And Allah knows best.