Practise Discovery and development of drugs. 14 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Where medicines come from (plants, microorganisms and chemists' laboratories) and how a new drug is tested before it can be used: preclinical testing, clinical trials, placebos, double blind trials and peer review. A common 4 to 6 mark 'describe' question, and a good source of data questions.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Match drugs to their original sourcesDigitalis from foxgloves, aspirin from willow, and penicillin from Penicillium mould (discovered by Alexander Fleming).
4
State what new drugs are tested forToxicity (is it harmful?), efficacy (does it work?) and dose (how much should be given?).
5
Describe preclinical testingThe drug is tested in a laboratory on cells, tissues and live animals before any people take it.
5
Describe the stages of clinical trialsVery low doses are given first to check safety; further trials on patients find the optimum dose.
6
Explain why a placebo is usedA placebo contains no drug, so comparing the two groups shows whether the drug itself has an effect.
6
Explain why results are peer reviewedOther experts check the method, results and conclusions before publication, so false or biased claims are less likely to be published.
7
Explain why double blind trials are usedNeither doctors nor patients know who has the drug, so their expectations cannot bias the results.
Notes
Where drugs come from
Traditionally, drugs were extracted from plants and microorganisms.
The heart drug digitalis comes from foxgloves. The painkiller aspirin comes from willow.
Penicillin was discovered by Alexander Fleming from the Penicillium mould. He noticed that bacteria did not grow around some mould that had got onto one of his culture plates.
Most new drugs are now synthesised by chemists in the pharmaceutical industry, but the starting point may still be a chemical extracted from a plant.
Testing a new drug
New drugs must be tested and trialled to check that they are safe and effective. They are tested for toxicity (harm), efficacy (how well they work) and dose.
Preclinical testing is done in a laboratory using cells, tissues and live animals. Animals show the effect of the drug on a whole body.
Clinical trials use healthy volunteers and patients.
Very low doses are given at the start of a clinical trial, to check that the drug is safe.
If the drug is safe, further clinical trials find the optimum dose: the dose that works best with the fewest side effects.
Placebos and double blind trials
A placebo looks like the drug but does not contain the drug. In a trial, some patients get the drug and some get the placebo.
Some patients feel better just because they believe they are being treated, so comparing the two groups shows whether the drug has a real effect.
In a double blind trial, neither the doctors nor the patients know who has received the drug and who has received the placebo until the trial is complete. This stops their expectations affecting the results.
Publishing the results
The results are published only after peer review: other scientists who are experts in the same field check the method, results and conclusions.
This makes it less likely that false or biased claims are published.
Cheatsheet
Digitalis (heart drug) ← foxgloves
Aspirin (painkiller) ← willow
Penicillin ← Penicillium mould, discovered by Alexander Fleming
New drugs are tested for toxicity, efficacy and dose
Preclinical testing: cells, tissues and live animals
Clinical trials: healthy volunteers and patients; very low doses first, then find the optimum dose
Placebo = looks like the drug but contains no drug
Double blind: neither doctors nor patients know who gets the drug or the placebo
Peer review: other experts check the results before they are published
How to answer each type of question
Recall: sources of drugs
1 mark each3
Learn the three pairs: foxglove → digitalis, willow → aspirin, Penicillium → penicillin.
Remember who discovered penicillin: Alexander Fleming.
Example. Give the original source of each drug. (a) Aspirin (b) Digitalis (c) Penicillin
Start with preclinical testing: cells and tissues, then live animals.
Clinical trials: very low doses first to check safety, then patients to find efficacy and the optimum dose.
Mention the placebo and the double blind design.
Finish with peer review before the results are published.
Example. A company has developed a new drug to lower blood pressure. Describe how the drug would be tested before doctors could use it. (6 marks)
Show the model answer
The drug is first tested in a laboratory on cells and tissues, to check that it is not toxic. It is then tested on live animals, to see its effect on a whole body. If it seems safe, clinical trials start: very low doses are given to healthy volunteers to check for harmful side effects. The drug is then given to patients with high blood pressure to find out whether it works and to find the optimum dose. Some patients are given a placebo instead, and the trial is double blind, so neither the doctors nor the patients know who has the drug. Other scientists check the results (peer review) before they are published. This is a Level 3 answer (5 to 6 marks): the stages are in a logical order and linked to what each one tests. A list of stages with no detail would be Level 1 or 2.
Explain placebos and double blind trials
2 to 3 marks7
Placebo: looks like the drug but contains no drug.
Double blind: neither the doctors nor the patients know who has the drug.
Give the reason: so expectations cannot bias the results.
Example. In a trial of a new painkiller, half the patients were given a placebo. The trial was double blind. (a) What is a placebo? (b) Explain why the trial was double blind.
Show the model answer
(a) A substance that looks like the drug but does not contain the drug (1) (b) Neither the doctors nor the patients knew who had the drug (1), so the doctors' and patients' expectations could not affect (bias) the results (1).
Data: results of a clinical trial
2 to 3 marks7
Percentage = number improved ÷ number in the group × 100.
Compare the drug group with the placebo group.
Explain any improvement in the placebo group.
Example. In a trial, 200 patients took a new drug and 200 patients took a placebo. Symptoms improved in 138 of the patients who took the drug and 46 of the patients who took the placebo. (a) Calculate the percentage of patients whose symptoms improved in each group. (b) Suggest why some patients who took the placebo improved.
Show the model answer
(a) Drug: 138 ÷ 200 × 100 = 69% (1); placebo: 46 ÷ 200 × 100 = 23% (1) (b) They believed they were being treated, so they felt better (the placebo effect), or they would have recovered anyway (1).