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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

Safety

This is important as some drugs are toxic, and have other side effects that might be harmful to people

Effectiveness

This is also known as efficacy, and checks how well the drug cures the disease, or improves symptoms.

Dosage

This varies, and has to be closely controlled, as too high a concentration might be toxic.

Three stages of testing drugs

There are three main stages of testing:

1. The drugs are tested using computer models and skin cells grown using human stem cells in the laboratory. This allows the efficacy and possible side effects to be tested. Many substances fail this first test of a preclinical drug trial because they damage cells or do not seem to work.
2. Drugs that pass the first stage are tested on animals in the second part of a preclinical drug trial. 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.
3. Drugs that have passed animal tests are used in human 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.