Discovery and development of drugsSpec 4.3.1.9
In short
Drugs were traditionally extracted from plants and microorganisms, such as digitalis from foxgloves and aspirin from willow, but most new drugs are now synthesised by chemists. New drugs are tested for toxicity, efficacy and dose: first in preclinical testing on cells, tissues and live animals, then in clinical trials on healthy volunteers and patients.
Where drugs come from
Traditionally, drugs were extracted from plants and microorganisms.
- The heart drug digitalis originates from foxgloves.
- The painkiller aspirin originates from willow.
- Penicillin was discovered by Alexander Fleming from the Penicillium mould.
Most new drugs are synthesised by chemists in the pharmaceutical industry. However, the starting point may still be a chemical extracted from a plant.
Testing and trialling
New medical drugs have to be tested and trialled before being used, to check that they are safe and effective. They are extensively tested for:
- Toxicity
- How harmful the drug is to cells and the body.
- Efficacy
- How well the drug works to treat the condition.
- Dose
- The amount of drug to give so that it works without causing harm.
- Preclinical testing is done in a laboratory using cells, tissues and live animals.
- Clinical trials use healthy volunteers and patients.
- Very low doses of the drug are given at the start of the clinical trial.
- 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.
A placebo looks like the drug but contains no active drug. In a double blind trial, neither the patients nor the doctors know who has the real drug and who has the placebo until the end. This stops expectations affecting the results.
Peer review
The results of testing and trials are published only after scrutiny by peer review. Other scientists check the methods and conclusions before they are published.
Preclinical comes first and uses cells, tissues and animals. Clinical trials come second and use people. Do not swap them.
Quick check
Name the four types of pathogen.
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Viruses, bacteria, protists and fungi.
Name the three ways white blood cells defend against pathogens.
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Phagocytosis, antibody production and antitoxin production.
Why can antibiotics not be used to treat a viral disease?
Show answer
Antibiotics cannot kill viral pathogens.
What does a vaccine contain?
Show answer
Small quantities of dead or inactive forms of a pathogen.
Where is preclinical testing carried out, and on what?
Show answer
In a laboratory, using cells, tissues and live animals.
Written and checked against the AQA GCSE Biology (8461) specification · Updated October 2026