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New drugs need to be tested and trialled before doctors prescribe them and patients take them. This allows drugs to be checked for:

• safety
• effectiveness
• dosage

Three stages of testing drugs

There are three main stages of testing:

Preclinical drug trials

• The drugs are tested using computer models and human cells grown in the laboratory. This allows the effectiveness to be tested and if the drug is safe to use on living cells. Many substances fail this test because they damage cells or do not seem to work.

Animal testing

• Drugs that pass the first stage are tested on animals. In the UK, new medicines have to undergo these tests. But it is illegal to test cosmetics and tobacco products on animals. A typical test involves giving a known amount of the substance to the animals, then monitoring them carefully for any side-effects.

Human clinical trials

• Drugs that have passed animal tests are used in clinical trials. They are tested on healthy volunteers to check that they are safe. The substances are then tested on people with the illness to ensure that they are safe and that they work. Low doses of the drug are used initially, and if this is safe the dosage increases until the optimum dosage is identified.
• Placebos, inactive versions of the drug, are used. Volunteers are split into groups, some receive the drug and others receive the placebo. It is important they do not know which they are taking. This is called a blind trial. Often, a double-blind trial is carried out where the doctor giving the patient the drug is also unaware. Results from the groups are compared to ensure that the drug is having an effect and that any changes are not due the experimental trial process.

There are obvious benefits to testing drugs but some people consider drug trials to be dangerous and animal testing to be unethical.

The importance of drug testing - Thalidomide

Thalidomide is a medical drug that caused unexpected and serious damage to unborn babies in the 1950s and 1960s. Thalidomide was developed as a sleeping pill, but it was also thought to be useful for easing morning sickness in pregnant women. Unfortunately, it had not been tested for use in this way.

Birth defects

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.

Thalidomide today

Thalidomide is now used as a treatment for leprosy and bone cancer. Its use is heavily regulated, however, to prevent a repeat of the problems it caused in the last century.

Learn more about drug discovery with Dr Alex Lathbridge.

Listen to the full series on ����ý Sounds.