Common Registration Assessment, Part 1

Haloperidol oral solution volumes and daily dose maximums for the GPhC assessment

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

Published 6 November 2026. Independent revision material, not GPhC questions, not for patient care.

A dropper releasing liquid into an amber glass bottle
Photo from Pexels, used under the Pexels licence. It is a stock image and does not show the exercise.

The manufacturer's UK product information for haloperidol 2 mg/ml oral solution states that the solution contains 2 mg of haloperidol in each millilitre, and gives a conversion table: 0.5 mg is 0.25 ml, 1 mg is 0.5 ml, 2 mg is 1 ml, 5 mg is 2.5 ml, 10 mg is 5 ml, 15 mg is 7.5 ml and 20 mg is 10 ml.

The same information states that for the treatment of schizophrenia and schizoaffective disorder the dose is 2 to 10 mg a day orally, as a single dose or in 2 divided doses, and that the maximum dose is 20 mg a day.

It also states that the oral solution in a bottle with an oral syringe is intended to be used for single doses of 0.5 mg haloperidol and above, equivalent to 0.25 ml and above.

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 a supply period. All prescriptions and patients here are fictional; these are revision materials, not for patient care.

The method

  1. Identify the stated dose in milligrams.
  2. Divide the dose in milligrams by the 2 mg per ml concentration for the volume in millilitres.
  3. For divided doses, calculate the volume per dose and per day separately.
  4. Keep milligrams and millilitres separate; convert only when the question asks.

Three practice questions

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

Question 1

A fictional patient is prescribed a single 5 mg dose of haloperidol using the 2 mg/ml oral solution. How many millilitres is this?

Show the answer

Answer: 2.5 ml

Working: 5 mg / 2 mg per ml = 2.5 ml.

Question 2

A fictional patient takes 10 mg a day in 2 divided doses using the 2 mg/ml oral solution. How many millilitres do they take in total each day?

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Answer: 5 ml

Working: 10 mg a day / 2 mg per ml = 5 ml each day, which is 2.5 ml in each of the two divided doses.

Question 3

A fictional patient takes the maximum stated dose for schizophrenia of 20 mg a day using the 2 mg/ml oral solution. How many millilitres is this each day?

Show the answer

Answer: 10 ml

Working: 20 mg / 2 mg per ml = 10 ml each day.

eMC SmPC: HALDOL 2 mg/ml oral solution

https://www.medicines.org.uk/emc/product/15252/smpc

Where marks are lost

  • Reading millilitres as milligrams from the conversion table.
  • Halving the daily total for the divided doses but forgetting the question asks for the whole day.
  • Rounding volumes instead of using the exact 2 mg per millilitre conversion.

Frequently asked questions

Are these official assessment questions?

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

Does this calculation decide a real haloperidol dose?

No. Follow the stated prescription in the exercise. Real dosing depends on the condition being treated, age and response, with lower doses in elderly patients.

How should I check the answer?

Check the requested unit, then work backwards from the volume to the stated dose in milligrams.

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.