A 29-year-old man is preparing for a long journey across several countries, during which he expects to spend many hours on buses and ferries. He reports that he frequently becomes nauseated during long rides and wants advice on the best medication to prevent this. He takes no regular medication and has no illnesses.
Which drug would provide the greatest relief from his travel-related symptoms?

A. Cinnarizine
B. Cyclizine
C. Scopolamine (Hyoscine)
D. Metoclopramide
E. Promethazine

Correct Answer: C — Hyoscine (Scopolamine)

Detailed Explanation

Why motion sickness occurs

Motion sickness arises when the brain receives conflicting sensory inputs:

The inner ear (vestibular system) detects motion.
The eyes may not detect the same motion.
This sensory mismatch activates the vomiting centre.

Most effective drug: Hyoscine

Hyoscine (scopolamine) is an antimuscarinic that blocks M1 receptors in the vestibular nuclei and vomiting centre.

Highest efficacy for motion sickness (BNF).
Comes as oral form or transdermal patch (useful for long travel).
Side-effects: dry mouth, blurred vision, urinary retention, confusion (avoid in elderly, glaucoma, BPH).

Comparison of options

Drug	Class	Effectiveness	Notes
Hyoscine	Antimuscarinic	⭐⭐⭐⭐⭐ Most effective	Best prophylaxis; strong anticholinergic effects.
Cyclizine	H1 antihistamine (piperazine)	⭐⭐⭐	Good first-line if hyoscine contraindicated.
Cinnarizine	H1 antihistamine + calcium channel blockers	⭐⭐	Mild; used in vertigo/Ménière’s.
Promethazine	Sedating antihistamine	⭐⭐	Works but causes sedation; poor compliance for travellers.
Metoclopramide	Dopamine antagonist	⭐	Helps nausea but not effective for true motion sickness.

Extra high-level MRCP points

Motion sickness responds poorly to dopamine antagonists (metoclopramide, prochlorperazine).
Antimuscarinics block vestibular pathways → best efficacy.
Histamine pathways also contribute → antihistamines help but are weaker.
Transdermal hyoscine delivers slow release for 72 hours, ideal for long sea/bus journeys.

Cheat Sheet (Exam-Ready)

Pathophysiology

Sensory conflict → vestibular mismatch → vomiting centre activation.

First-line MOST EFFECTIVE

Hyoscine (scopolamine).

Alternative Options

Cyclizine → preferred antihistamine (non-sedating).
Cinnarizine → mild effect.
Promethazine → sedating antihistamine.
Metoclopramide → NOT useful for vestibular nausea.

When to avoid hyoscine

Elderly
Glaucoma
BPH
Cognitive impairment

Practical

Patch = 72 hours coverage.
Give medicine before travel (prophylaxis > treatment).

20 Flashcards

1. Q: What causes motion sickness?
A: Sensory mismatch between visual and vestibular inputs.

2. Q: Most effective drug for motion sickness?
A: Hyoscine (scopolamine).

3. Q: Mechanism of hyoscine?
A: M1 muscarinic receptor antagonist.

4. Q: Why is hyoscine superior?
A: Direct action on vestibular pathways → strongest efficacy.

5. Q: Duration of hyoscine patch?
A: Up to 72 hours.

6. Q: Major side-effects of hyoscine?
A: Dry mouth, blurred vision, confusion, urinary retention.

7. Q: Which antihistamine is preferred for motion sickness?
A: Cyclizine.

8. Q: Cinnarizine is used mainly for?
A: Vertigo and Ménière’s disease.

9. Q: Promethazine disadvantage?
A: Sedation.

10. Q: Is metoclopramide useful for motion sickness?
A: No, because vestibular pathways use ACh and histamine, not dopamine.

11. Q: Drug class of cyclizine?
A: H1 antihistamine + anticholinergic activity.

12. Q: Drug class of cinnarizine?
A: H1 blocker + calcium channel antagonist.

13. Q: Scopolamine contraindication?
A: Narrow-angle glaucoma.

14. Q: When should prophylaxis be taken?
A: Before starting the journey.

15. Q: Which drug is best for long boat/ferry trips?
A: Hyoscine patch.

16. Q: Why antihistamines help?
A: Vestibular system uses histamine pathways.

17. Q: Mechanism of promethazine?
A: H1 blocker with strong sedation.

18. Q: What is the vestibular nerve role in motion sickness?
A: Sends conflicting movement signals.

19. Q: Which drug may reduce motion sickness but causes marked sedation?
A: Promethazine.

20. Q: Which drug should NOT be relied upon for motion sickness?
A: Metoclopramide.

MCQs for Practice

1. A traveller wants a medicine for motion sickness. Which receptor primarily mediates the most effective therapy?

A. Dopamine
B. Serotonin
C. Muscarinic
D. NK-1
E. GABA
Answer: C

2. A man with glaucoma needs motion sickness prophylaxis. Best option?

A. Hyoscine
B. Cyclizine
C. Scopolamine patch
D. Promethazine
E. Metoclopramide
Answer: B

3. Which drug is least effective for true vestibular motion sickness?

A. Hyoscine
B. Cyclizine
C. Promethazine
D. Metoclopramide
E. Cinnarizine
Answer: D

4. Scopolamine mainly works on which brain area?

A. Area postrema
B. Vestibular nuclei
C. Frontal cortex
D. Cerebellar cortex
E. Raphe nuclei
Answer: B

5. Which one is most sedating among motion sickness drugs?

A. Cyclizine
B. Cinnarizine
C. Hyoscine
D. Promethazine
E. Metoclopramide
Answer: D

Summary (10–20 sentences)

Motion sickness develops when the brain receives conflicting signals from the eyes and the vestibular system, leading to activation of the vomiting centre. The most effective pharmacological treatment is hyoscine, an antimuscarinic drug that blocks M1 receptors involved in vestibular transmission. It is recommended by the BNF as the strongest option, especially for prophylaxis on long journeys. A transdermal patch can provide steady relief for up to three days, making it ideal for travel. However, hyoscine causes anticholinergic side-effects such as dry mouth, blurred vision, urinary retention, and confusion; therefore, it should be avoided in patients with glaucoma, BPH, or cognitive impairment. When hyoscine is unsuitable, antihistamines are preferred alternatives. Cyclizine is the most commonly used antihistamine for motion sickness due to its moderate efficacy and relatively low sedation. Cinnarizine can also help but is weaker and more suited for vertigo-related disorders. Promethazine is effective but highly sedating, limiting its practicality for travellers. Metoclopramide is least effective because vestibular-mediated nausea does not depend on dopamine pathways. All medications are more effective when given before travel, as prophylaxis works better than treating symptoms once they begin. Understanding receptor pathways—muscarinic and histamine—is key to answering MRCP questions on motion sickness.