Traditionally, drugs were extracted from plants and microorganisms. The heart drug digitalis originates from foxgloves, the painkiller aspirin originates from willow, and 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 have to be tested and trialled before use, to check that they are safe and effective. They are extensively tested for toxicity, efficacy and dose. Preclinical testing is done in a laboratory using cells, tissues and live animals.
Clinical trials then use healthy volunteers and patients. A very low dose of the drug is given at the start. If the drug is found to be safe, further clinical trials are carried out to find the optimum dose. In double blind trials, some patients are given a placebo, so neither the patients nor the doctors know who has the real drug.
The results of testing and trials are published only after scrutiny by peer review, when other scientists check the work.