Traditionally, drugs were extracted from plants and microorganisms. The heart drug digitalis comes from foxgloves, and the painkiller aspirin comes from willow. Penicillin was discovered by Alexander Fleming from the Penicillium mould. Today most new drugs are synthesised by chemists in the pharmaceutical industry, although the starting point may still be a chemical extracted from a plant.
New drugs must be tested and trialled before use, to check that they are safe and effective. They are extensively tested for toxicity (is it harmful?), efficacy (does it work?) and dose (how much is needed?).
Preclinical testing is done in a laboratory using cells, tissues and live animals. Then clinical trials use healthy volunteers and patients. Very low doses are given at the start. If the drug is found to be safe, further clinical trials find the optimum dose. In a double blind trial, some patients are given a placebo, a substance that contains no drug. Neither the patients nor the doctors know who has the real drug until the trial ends.
The results of testing and trials are published only after scrutiny by other scientists, which is called peer review.