Common Registration Assessment, Part 1
Co-codamol strengths and 24-hour maximums for the GPhC assessment
Three original practice questions, with the working shown. Read the stated prescription or plan before calculating.
Published 16 October 2026. Independent revision material, not GPhC questions, not for patient care.
The NHS lists three co-codamol strengths: 8/500, 15/500 and 30/500. The first number is mg of codeine and the second is mg of paracetamol in each tablet. Adults can take 1 or 2 tablets up to 4 times in 24 hours, leaving at least 4 to 6 hours between doses.
The maximum dose is 8 tablets in 24 hours, whichever strength is used. The paracetamol inside co-codamol is what makes exceeding the maximum dangerous.
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
- Identify the exact formulation, strength, dose and frequency supplied in the question.
- Convert an X mg/5 mL strength to mg/mL if a dose-to-volume conversion is needed.
- Calculate one dose first; for tablets or capsules divide prescribed mg by mg per unit.
- Scale to the stated frequency and duration only when a total quantity is requested.
- 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 dose is 2 tablets of co-codamol 30/500. How much codeine and how much paracetamol is in that one dose?
Show the answer
Answer: 60 mg codeine and 1000 mg (1 g) paracetamol
Working: 2 × 30 = 60 mg codeine. 2 × 500 = 1000 mg paracetamol, and 1000 ÷ 1000 = 1 g.
Question 2
Using any strength of co-codamol, what is the maximum amount of paracetamol from co-codamol alone in 24 hours?
Show the answer
Answer: 4000 mg (4 g)
Working: The maximum is 8 tablets in 24 hours. 8 × 500 = 4000 mg, and 4000 ÷ 1000 = 4 g.
Question 3
A fictional adult takes 2 tablets of co-codamol 15/500 four times in 24 hours. How many tablets is that, and how much codeine does the day contain?
Show the answer
Answer: 8 tablets and 120 mg codeine
Working: 2 × 4 = 8 tablets, which is the stated 24-hour maximum. 8 × 15 = 120 mg codeine.
NHS: How and when to take co-codamol for adults
https://www.nhs.uk/medicines/co-codamol-for-adults/how-and-when-to-take-co-codamol-for-adults/
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
Try 15 free questions with worked answers. No sign-up required.
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See also the formula sheet, the eight sample questions and the approved calculator page.