Common Registration Assessment, Part 1

Co-dydramol strengths and 24-hour tablet maximums for the GPhC assessment

Three original practice questions, with the working shown. Read the stated prescription or plan before calculating.

Published 28 October 2026. Independent revision material, not GPhC questions, not for patient care.

Multicoloured pills in plastic blister packs
Photo from Pexels, used under the Pexels licence. It is a stock image and does not show the exercise.

The NHS lists co-dydramol tablets containing 7.46 mg, 10 mg, 20 mg or 30 mg of dihydrocodeine with 500 mg of paracetamol; a packet marked 10/500 means 10 mg dihydrocodeine and 500 mg paracetamol per tablet.

The NHS lists the maximum dose for adults and young people aged 16 and over as 8 tablets over 24 hours.

Each question fixes the values needed for its arithmetic. Write the unit beside every step and distinguish a single dose from a daily total or course supply. All prescriptions and patients here are fictional; these are revision materials, not for patient care.

The method

  1. Identify the exact formulation, strength, dose and frequency supplied in the question.
  2. Convert an X mg/5 mL strength to mg/mL if a dose-to-volume conversion is needed.
  3. Calculate one dose first; for tablets or capsules divide prescribed mg by mg per unit.
  4. Scale to the stated frequency and duration only when a total quantity is requested.
  5. Apply whole-container or complete-day rounding only if the question specifies it.

Three practice questions

Work each one on paper first, then open the answer. All patients and prescriptions are fictional.

Question 1

A fictional prescription specifies co-dydramol 10/500, 2 tablets four times a day. How many tablets is that in 24 hours, and does it reach the NHS maximum?

Show the answer

Answer: 8 tablets, exactly at the 8-tablet maximum

Working: 2 × 4 = 8 tablets; the NHS maximum is 8 tablets over 24 hours.

Question 2

A fictional dose is 2 tablets of co-dydramol 10/500. How much dihydrocodeine and how much paracetamol is in that one dose?

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Answer: 20 mg dihydrocodeine and 1,000 mg paracetamol

Working: 2 × 10 mg = 20 mg dihydrocodeine; 2 × 500 mg = 1,000 mg paracetamol.

Question 3

A fictional prescription uses co-dydramol 20/500 at 1 tablet twice a day. How much dihydrocodeine is taken in 24 hours?

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Answer: 40 mg

Working: 2 × 20 mg = 40 mg dihydrocodeine.

NHS: How and when to take co-dydramol

https://www.nhs.uk/medicines/co-dydramol/how-and-when-to-take-co-dydramol/

Where marks are lost

  • Using a remembered strength or schedule instead of the stated product.
  • Reporting a daily total when the question asks for one dose or the course.
  • Treating arithmetic as evidence that a real prescription is clinically suitable.

Frequently asked questions

Are these official assessment questions?

No. They are original revision exercises, not official GPhC questions and not for patient care.

Can a quantity calculation justify a formulation switch?

No. Follow the formulation and prescription in the exercise. Real switches and dose changes need clinical checks.

How should I check the answer?

Check the requested unit, then work backwards from the quantity to the stated dose and duration.

Sources

The questions above are original and use fictional patients and prescriptions. PreRegExamPrep is not affiliated with or endorsed by the General Pharmaceutical Council.

Practise until the method is automatic

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More calculation topics

See also the formula sheet, the eight sample questions and the approved calculator page.