Willow bark has been used for thousands of years to relieve pain. Scientists identified the active ingredient in willow bark as salicylic acid. They then developed aspirin, a related compound, which is used as a modern medicine. Explain why scientists developed aspirin rather than using salicylic acid directly as a medicine, and describe the steps that must be carried out before aspirin can be approved for use as a medicine.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Willow bark has been used for thousands of years to relieve pain. Scientists identified the active ingredient in willow bark as salicylic acid. They later synthesised aspirin, a related compound, which causes fewer side effects than salicylic acid.
Model answer (5 marks)
Scientists developed aspirin because salicylic acid irritates the stomach lining, causing pain and bleeding; aspirin is a pro‑drug that is less irritating.
1. In vitro studies are carried out on cells or tissues to confirm the anti‑inflammatory effect and to check for cytotoxicity.
2. Animal experiments are then performed to assess safety, toxicity and to determine a safe dose range.
3. Human clinical trials are conducted in phases: Phase I tests safety and dosage in a small group of healthy volunteers; Phase II evaluates efficacy and side‑effects in a larger patient group; Phase III confirms effectiveness and monitors adverse reactions in a large, diverse population.
4. A double‑blind, placebo‑controlled design is used in the trials so that neither the patient nor the researcher knows who receives aspirin, eliminating bias.
5. Only after successful trials and regulatory approval can aspirin be marketed as a medicine.
1. In vitro studies are carried out on cells or tissues to confirm the anti‑inflammatory effect and to check for cytotoxicity.
2. Animal experiments are then performed to assess safety, toxicity and to determine a safe dose range.
3. Human clinical trials are conducted in phases: Phase I tests safety and dosage in a small group of healthy volunteers; Phase II evaluates efficacy and side‑effects in a larger patient group; Phase III confirms effectiveness and monitors adverse reactions in a large, diverse population.
4. A double‑blind, placebo‑controlled design is used in the trials so that neither the patient nor the researcher knows who receives aspirin, eliminating bias.
5. Only after successful trials and regulatory approval can aspirin be marketed as a medicine.
Examiner tips
- Use the word ‘pro‑drug’ to explain reduced stomach irritation; mention the double‑blind placebo design; list the stages in the correct order; keep sentences short and use exam terminology such as ‘in vitro’, ‘in vivo’, ‘clinical trials’.
Common mistakes
- Confusing salicylic acid with aspirin as the same compound; not mentioning the double‑blind design; omitting the animal testing stage or the phases of clinical trials.
Mark scheme (5 marks)
- Salicylic acid causes side effects (such as irritation of the stomach / mouth), so aspirin was developed to reduce these side effects
- The new medicine must be tested in the laboratory / on cells or tissues to check it has the desired effect and is not harmful
- The medicine must be tested on animals to check for safety / toxicity and to determine appropriate doses
- Clinical trials must be carried out on human volunteers / patients to test for safety, effectiveness, and optimum dosage
- A double-blind trial / placebo is used so that neither the patient nor the doctor knows who has received the medicine, to avoid bias in the results
Key terms in this question
Related
- All OCR A-Level Chemistry B: Salters (H433) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More What's in a medicine? questions
- A pharmaceutical company is developing a new painkiller from a plant extract. Be…
- A scientist is researching a new antifungal medicine extracted from soil bacteri…
- A student reads about the development of penicillin. Alexander Fleming noticed i…
- A student is researching the history of medicines. They discover that for centur…