Carbimazole and Propylthiouracil (PTU) in Thyrotoxicosis
You have a condition called Thyrotoxicosis caused by an overactive thyroid gland.
Carbimazole (trade name NEOMERCAZOLE) and Propylthiouracil (known as PTU) are drugs prescribed to control the overactivity of the thyroid gland.
These drugs have been used safely for many years, and side effects are rare.
How do I take it?
Carbimazole is available as tablets containing 5 mg and 20 mg.
Treatment is started at high dosage, often 20 to 40 mg per day taken as one dose and is maintained until the patient’s thyroid returns to normal activity. The dosage is then gradually decreased to maintain normal thyroid activity. This maintenance dosage can vary from patient to patient in the range of 5 to 15 mg per day which may be taken as a single daily dosage.
Propylthiouracil is available as tablets containing 50mg.
Treatment is started at 200 to 400mg per day in divided doses until the patient’s thyroid returns to normal activity then reduced to 50 to 150 mg per day in divided doses. Initial dose may be gradually reduced to the maintenance dose.
Therapy is usually continued for 12 to 24 months.
What are the side effects?
Adverse reactions if they occur are usually seen in the first eight weeks of treatment:
- Headaches, nausea, joint pains, stomach upset
- Skin rashes are common in possibly 1 in 50 patients. If they occur contact your doctor
A rare side effect is bone marrow suppression which can present in 1 in 1000 patients. This presents as a severe sore throat, mouth ulcers, excessive bruising, unexplained fever, or a skin rash. If any of these symptoms occur stop taking Carbimazole or PTU and get a full blood test within 24 hours with your GP or ‘out of hours’ service. Please bring this leaflet with you.
The suppression of the bone marrow is often temporary with the bone marrow recovering after 1 to 2 weeks.
If the test shows that the white blood cells and platelets are normal you can restart the carbimazole straight away as before.
Carbimazole and PTU during pregnancy
It is recommended that you do not get pregnant whilst taking Carbimazole or PTU as both medications can increase the risk to the unborn baby.
It is essential that you discuss your treatment with your consultant/Specialist nurse before conception. Although it is possible to have a successful pregnancy whilst taking these medications.
Please note: Of course, sore throats, mouth ulcers and skin rashes are very common, and it is most likely that if you get one of these symptoms it is not the Carbimazole or PTU. However, the safest course of action is to stop taking the Carbimazole or PTU temporarily until you have had the results of your blood test.
If you are ever in doubt about what to do, please contact the endocrinology department on the telephone numbers in this leaflet or contact your own GP.
Contact Information
Normal working hours (Monday to Friday): the endocrine team (all telephone numbers are direct to consultant’s secretaries). At other times (5pm to 9pm) or in case of emergency or urgent advice being required, you should contact your own GP or go to your local Accident and Emergency department.
The Royal Oldham Hospital
Dr BM Mishra, Dr A Shiraz, Dr Ansari
Telephone:0161 778 5431
Email: Nafisa.Rafiq@nca.nhs.uk
Dr S Irshad, Dr W Ilyas, Dr E Mumdzic and Dr V Kaluarachchi
Telephone: 0161 627 8778
Fairfield General Hospital
Dr S Rowles, Dr L Pichaipillai and Dr S Kouta
Telephone: 0161 778 2676
Email: Lisa.Mills@nca.nhs.uk Dr P Elisaus and Dr H Khan
Telephone: 0161 778 2546
Email: Katharine.Clegg@nca.nhs.uk
Rochdale Infirmary
Dr PK Prakash
Telephone: 01706 517 032
Email: Tracey.Kirkbride@nca.nhs.uk
Endocrine Specialist Nurses
R Gilbert and N Hughes - 0161 627 8388
If English is not your first language and you need help, please contact the Interpretation and Translation Service on 0161 627 8770 or email interpretation@pat.nhs.uk
Northern Care Alliance NHS Group is Smoke Free – including all buildings, grounds, and car parks.
Stop smoking advice: 01706 517 522.
Patient Advice and Liaison Service (PALS): 0161 604 5897
Clinic appointments/clinical enquiries: 0161 624 0420
Date of Review: June 2026
Date of Next Review: June 2028
Ref No: PI_M_1090 (BRO)