# 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.

> OCR A-Level Chemistry B: Salters (H433) — WM What's in a medicine? · Explain · 5 marks

> 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.

## Mark scheme (5 marks)

1. Salicylic acid causes side effects (such as irritation of the stomach / mouth), so aspirin was developed to reduce these side effects
2. The new medicine must be tested in the laboratory / on cells or tissues to check it has the desired effect and is not harmful
3. The medicine must be tested on animals to check for safety / toxicity and to determine appropriate doses
4. Clinical trials must be carried out on human volunteers / patients to test for safety, effectiveness, and optimum dosage
5. 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

- [active ingredient](https://www.gradenine.co.uk/glossary/active-ingredient)

## Related

- [Revision notes for OCR A-Level Chemistry B: Salters (H433)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/willow-bark-has-been-used-for-e89b0cb0) · Published by Druglandscape Ltd.