A student is researching the history of medicines. They discover that for centuries, people chewed the leaves of the coca plant to reduce hunger and tiredness. Later, scientists isolated cocaine from the plant and used it as a local anaesthetic. Today, cocaine is no longer used as a medicine and has been replaced by safer synthetic drugs such as lidocaine. Explain why cocaine is no longer used as a medicine and describe the advantages of using synthetic drugs instead of plant extracts.

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

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

For centuries, indigenous peoples of South America chewed coca leaves for their stimulant effects. In the 19th century, cocaine was isolated from coca leaves and used medically as a local anaesthetic. It has since been replaced by synthetic local anaesthetics.

Model answer (5 marks)

Cocaine has harmful side effects, is addictive and toxic, so it is no longer used as a medicine.
Medicines must be safe and must be tested for safety before approval.
Synthetic drugs can be produced in a laboratory and manufactured on a large scale.
They can be designed or modified to reduce side effects or increase effectiveness.
Synthetic drugs give a purer and more consistent product than plant extracts.

Examiner tips

  • Use the exact terms from the mark scheme – harmful side effects, addictive, toxic, safe, tested, large scale, designed, purer, consistent.
  • Show the logical sequence: safety → production → design → quality.
  • Keep each point brief but complete.
  • Use UK spelling (e.g., ‘synthesised’ if you prefer, but ‘synthetic’ is fine).

Common mistakes

  • Confusing ‘addictive’ with ‘toxic’ – both are required. Failing to mention the need for safety testing. Using vague terms like ‘better’ instead of ‘purer’ or ‘more consistent’.

Mark scheme (5 marks)

  1. Cocaine has harmful side effects / is addictive / is toxic
  2. Medicines must be safe to use / must be tested for safety before being approved
  3. Synthetic drugs can be made in a laboratory / manufactured on a large scale
  4. Synthetic drugs can be designed / modified to reduce side effects or increase effectiveness
  5. Synthetic drugs give a purer / more consistent product compared to plant extracts

Key terms in this question

synthetic drug · plant extract · medicine

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