Sources of drug discovery

Medicines have traditionally been obtained from substances produced by plants and microorganisms. These natural sources can contain chemicals that have useful effects in the body.

• Digitalis, a heart drug, originates from foxglove plants.
• Aspirin, a painkiller, was developed from compounds associated with willow.
• Penicillin was discovered by Alexander Fleming from Penicillium mould, a microorganism.

Most new drugs are now synthesised by chemists in the pharmaceutical industry rather than obtained directly from natural sources. Plants can still provide a starting point: a chemical extracted from a plant may be used to develop a new drug.

Clinical drug trials

Clinical trials test potential medicines in people to find out whether they are safe, whether they have the intended effect and what dose should be used. They involve healthy volunteers and patients.

Clinical trials: safety and dose

Trials begin with very low doses to reduce the risk of harmful effects. If the drug is found to be safe, further trials investigate the optimum dose: a dose that produces the intended effect while keeping harmful effects acceptably low. A dose that is too low may not have the intended effect, while a higher dose may increase harmful effects.

Placebos and double-blind trials

A placebo is a treatment that contains no active drug. Comparing results from people given the drug with results from people given the placebo helps researchers assess the drug’s effects.

In a double-blind trial, neither the participants nor the people administering the treatment know who is receiving the drug and who is receiving the placebo during the trial. This helps reduce bias when the results are assessed: expectations about the treatment are less likely to influence participants’ reports or the assessment of their responses.

Preclinical drug testing

Before a potential medicine is tested in people, it is investigated in the laboratory. This preclinical testing uses cells, tissues and live animals to gather evidence about the drug’s effects.

Researchers use these tests to investigate:

• Toxicity: whether the drug causes harmful effects.
• Effectiveness: whether the drug produces its intended effect.
• Dose: what amounts of the drug may be suitable for further testing.

Cells and tissues allow researchers to observe effects on particular parts of a living system. Tests in live animals can show effects in a whole organism. Together, the results help researchers decide whether there is enough evidence to proceed to clinical trials, in which the drug is tested in people.

Preclinical results cannot establish with certainty that a drug will be safe and effective in humans. Cells, tissues and other animals do not always respond to a drug in the same way as the human body.