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New drugs are being developed all the time. Historically, drugs have come from natural sources as parts of plants and micro-organisms have been extracted.

Plant extracts

Certain drugs that can be extracted from natural sources have been known about for a long time. For example, willow bark was used by the ancient Greeks to help cure fevers and pains. It was later discovered that the active ingredient was salicylic acid. This was modified by chemists into the substance we call aspirin, which is less irritating to the stomach than salicylic acid.

Plants are still important today, but most plant drugs are now created in a laboratory by scientists at pharmaceutical companies. These companies now have synthetic versions of the plant extracts, and use these as the starting point to develop new drugs.

New medical drugs have to be tested to ensure that they both work, and are safe, before they can be prescribed.

Stages of drug testing

The main stages of testing are preclinical and clinical.

Preclinical testing

The drugs are tested using computer models and human cells grown in the laboratory. Many substances fail this test because they damage cells or do not work.

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.

Clinical trials

Drugs that have passed animal tests are used in clinical trials. They are then tested on healthy volunteers to check that they are safe. If they are found to be safe, the substances are then tested on people with the illness to ensure that they work.

During clinical trials it needs to be determined if the drug is more effective than current treatments. This may involve asking the patient if they feel better or not. To avoid bias a number of strategies are applied.

• Placebo/Control – Clinical trials often involve one group who are given the drug which is being tested, and a control group who are given a placebo. A placebo is a pill that does not contain the active ingredient, and so should have no effect whatsoever on the patient.
• Blind trials – The patients are not told if they are in the trial group or the placebo/control group.
• Double blind trials – Neither the patient nor the doctor administering the drug knows if the patient is receiving the drug or a placebo in an attempt to eliminate bias altogether.