Developing new medicines

Health, disease and the development of medicines · Antibiotics, culturing microorganisms and new medicines · note 5 of 7

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In short

Developing a new medicine has four stages: discovery, development, preclinical testing and clinical testing. In preclinical testing the medicine is tested on cells, tissues and then live animals to check whether it is toxic and whether it works. In clinical testing it is given first to a few healthy volunteers, then to patients to find the right dose.

Developing a new medicine, including a new antibiotic, takes many stages. Each stage checks that the medicine is safe and that it works.

Discovery: finding a chemical that might treat the disease. These may come from natural sources, such as plants or microorganisms, or be designed in a laboratory.
Development: the chemical is studied and improved, and a way to make it as a medicine is worked out.
Preclinical testing: the medicine is tested in the laboratory on cells and tissues, and then on live animals, to find out if it is toxic and whether it works.
Clinical testing: the medicine is tested on people. It is first given to a small number of healthy volunteers to check it is safe, then to patients to check that it works and to find the right dose.

Only a medicine that passes all the stages can be used to treat patients. The testing protects people from harmful or ineffective medicines.

Exam tip:

Learn the four stages in order: discovery, development, preclinical, clinical. Preclinical comes before any testing on humans.

Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026

Frequently asked questions

Why can't antibiotics kill viruses?

Antibiotics cannot kill viruses because they work by inhibiting cell processes in bacteria, and viruses are not cells. Viruses live and reproduce inside host cells, so they do not have the cell processes that antibiotics target. This is why antibiotics cannot be used to treat viral diseases such as HIV, colds or flu.

What are the stages of developing a new medicine?

New medicines go through four stages: discovery of a chemical that might treat the disease, development to improve it, preclinical testing on cells, tissues and live animals to check toxicity and effectiveness, and clinical testing on people. Clinical testing starts with a few healthy volunteers to check safety, then patients to find the dose.

Why are bacterial cultures incubated at 25 °C?

Triple only Bacterial cultures are incubated at 25 °C because a lower temperature makes it less likely that harmful pathogens, which grow best at body temperature, will grow. The lid is taped on but not fully sealed, so microorganisms cannot escape or get in, but oxygen can still enter. The dish is incubated upside down.

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