Drugs are substances that change chemical reactions in the body. Medical drugs relieve disease and illness, and are extensively tested before being used. Recreational drugs such as alcohol and tobacco are taken by people because they like the effects they have on their bodies, but they may be addictive. Cannabis and heroin are illegal recreational drugs that are very addictive.

Clinical trials are not without risk. Sometimes severe and unexpected side effects occur. Most substances do not pass all of the tests and trials, so drug development is expensive and takes a long time.

Double blind trials aim to minimise the placebo effect. Some patients are given the drug while others are given a placebo. A placebo is designed to appear exactly the same as the drug itself, but it does not actually contain any of the drug. The doctors and patients are not told who have received the drug and who have received the placebo until the trial is over.

By 1960 thalidomide was found to damage the development of unborn babies, especially if it had been taken in the first four to eight weeks of pregnancy. The drug led to the arms or legs of the babies being very short or incompletely formed. More than 10,000 babies were affected around the world.
As a result of this disaster, thalidomide was banned. Drug testing was also made more rigorous than before.

Drugs change chemical processes in the body. People may become dependent on the drug or addicted to it, and may suffer withdrawal symptoms if they stop taking the drug.
Alcohol and nicotine (found in tobacco) are legal recreational drugs. However, misuse of them can cause health problems.

About 114,000 people die every year as a result of smoking-related illnesses. All cigarettes sold now carry a prominent health warning.
Nicotine is the addictive substance in tobacco smoke. It reaches the brain within 20 seconds and creates a dependency so that smokers become addicted. Smoking increases the risks of:
heart disease and strokes
miscarriage, premature birth and low birth weight
lung cancer, mouth cancer and throat cancer.

Heroin and cocaine are very addictive. Like ecstasy, they can damage the heart and circulatory system. Cannabis smoke contains chemicals that cause mental illness in some people.

A research report in 2006 classified various drugs according to their health and social risks, without reference to whether they are legal or not. In the report, heroin and cocaine are the most dangerous two drugs, alcohol is the fifth most dangerous and tobacco is ninth.

Some of these drugs are banned by law. Others are legally available on prescription or even in some medicines available from the pharmacy. However, the use of performance enhancing drugs is widely seen as unfair. They may also damage the athlete’s body.
Sporting regulations ban the use of performance enhancing drugs, and athletes are regularly tested to make sure that they are not using them.