POM-V Prescription Required Companion Animal

Felimazole 2.5 mg Coated Tablets for Cats

Active ingredient: Thiamazole

Form

Tablet

Species

Cats

Manufacturer

Dechra Regulatory B.V.

VMD MA No.

50406/3044

What it's used for

For the long term treatment of feline hyperthyroidism.

Full indications, dosage and side effects ↓

View official SPC (PDF)

The prescription itself has a price. See what practices near you charge for a consultation and the written prescription fee.

Paying less for Thiamazole

1

Ask your vet for a written prescription

They must provide one on request. Under the CMA Order the fee is capped at £21 from 2027.
2

Fill it at a registered online retailer

The CMA found online pharmacies 50–60% cheaper than practice dispensing on common medicines — typically £200–£300 a year.

Your prescription rights → VMD register of retailers →

Prescription required

Your vet must provide a written prescription on request. You can then purchase from any licensed online retailer.

Clinical information

Felimazole 2.5 mg Coated Tablets for Cats — SPC Details

Source: VMD Summary of Product Characteristics (SPC). Last updated 27 Mar 2026.

For the long term treatment of feline hyperthyroidism.

For the stabilisation of feline hyperthyroidism prior to surgical thyroidectomy and for the
long term treatment of feline hyperthyroidism, the recommended starting dose is 5 mg
per day.
Wherever possible, the total daily dose should be divided into two and administered
morning and evening. Tablets should not be split.
If, for reasons of compliance, once daily dosing with a 5 mg tablet is preferable, then
this is acceptable although the 2.5 mg tablet given twice daily may be more efficacious
in the short term. The 5 mg tablet is also suitable for cats requiring higher dose rates.
Haematology, biochemistry and serum total T4 should be assessed before initiating
treatment and after 3 weeks, 6 weeks, 10 weeks, 20 weeks, and thereafter every 3
months. At each of the recommended monitoring intervals, the dose should be titrated
to effect according to the total T4 and to clinical response to treatment. Dose
adjustments should be made in increments of 2.5 mg and the aim should be to achieve
the lowest possible dose rate.
If more than 10 mg per day is required animals should be monitored particularly
carefully.
The dose administered should not exceed 20 mg/day.
For long term treatment of hyperthyroidism the animal should be treated for life.
AN: 01884/2025 & 01900/2025Page 5 of 7

Do not use in cats suffering from systemic disease such as primary liver disease or
diabetes mellitus.
Do not use in cats showing signs of autoimmune disease.
Do not use in animals with disorders of white blood cells, such as neutropenia and
lymphopenia.
Do not use in animals with platelet disorders and coagulopathies (particularly
thrombocytopenia).
Do not use in in cases of hypersensitivity to the active substance or to any of the
excipients
Do not use in pregnant or lactating females (please refer to section 3.7).

Cats:
Uncommon
(1 to 10 animals / 1,000 animals
treated):
Vomiting
a
;
Anorexia
a
, Inappetence
a
, Lethargy
a
;
Pruritus
a,b
, Excoriation
a,b
;
Prolonged bleeding
a,c,d
;
Hepatopathy
a
, Icterus
a,d
;
Eosinophilia
a
, Lymphocytosis
a
, Neutropenia
a
,
Lymphopenia
a
, Leucopenia
a,e
, Agranulocytosis
a
,
Thrombocytopenia
a,g
, Haemolytic anaemia
a
.
Rare
(1 to 10 animals / 10,000
animals treated):
Serum anti-nuclear antibodies
f,h
, Anaemia
f,h
.Very rare
(<1 animal / 10,000 animals
treated, including isolated
reports):
Lymphadenopathy
f,h
.
a
Resolves within 7-45 days after cessation of thiamazole therapy.
b
Severe. Of the head and neck.
c
Sign of bleeding diathesis.
d
Associated with hepatopathy.
e
Slight.
f
Immunological side effect.
g
Occurs uncommonly as a haematological abnormality and rarely as an immunological
side effect.
h
Treatment should be stopped immediately and alternative therapy considered
following a suitable
period for recovery.
AN: 01884/2025 & 01900/2025Page 4 of 7
Adverse events have been reported following long term control of hyperthyroidism. In
many cases, signs may be mild and transitory and not a reason for withdrawal of
treatment.
The more serious effects are mainly reversible when medication is stopped.
Following long term treatment with thiamazole in rodents, an increased risk of neoplasia
in the thyroid gland has been shown to occur, but no evidence is available in cats.
Reporting adverse events is important. It allows continuous safety monitoring of a
veterinary medicinal product. Reports should be sent, preferably via a veterinarian, to
either the marketing authorisation holder or its local representative or the national
competent authority via the national reporting system. See the package leaflet for
respective contact details.

None.

Special precautions for safe use in the target species:
If more than 10 mg per day is required animals should be monitored particularly
carefully.
Use of the veterinary medicinal product in cats with renal dysfunction should be subject
to careful benefit-risk assessment by the clinician. Due to the effect thiamazole can
have on reducing the glomerular filtration rate, the effect of therapy on renal function
should be monitored closely as deterioration of an underlying condition may occur.
Haematology must be monitored due to risk of leucopenia or haemolytic anaemia.
Any animal that suddenly appears unwell during therapy, particularly if they are febrile,
should have a blood sample taken for routine haematology and biochemistry.
Neutropenic animals (neutrophil counts <2.5 x 10
/l) should be treated with prophylactic
bactericidal antibacterial drugs and supportive therapy.
As thiamazole can cause haemoconcentration, cats should always have access to
drinking water.
Please refer to section 3.9 for monitoring instructions.
Special precautions to be taken by the person administering the veterinary medicinal
product to animals
Wash hands after use.
AN: 01884/2025 & 01900/2025Page 3 of 7
In case of accidental ingestion, seek medical advice immediately and show the package
leaflet or the label to the physician.
Thiamazole may cause vomiting, epigastric distress, headache, fever, arthralgia,
pruritus and pancytopaenia. Treatment is symptomatic.
Wash hands with soap and water after handling litter used by treated animals.
Do not eat, drink or smoke while handling the tablet or used litter.
Do not handle this veterinary medicinal product if you are allergic to
products. If allergic symptoms develop, such as a skin rash, swelling of the face, lips or
eyes or difficulty in breathing, you should seek medical attention immediately and show
the package leaflet or the label to the physician.
Do not break or crush tablets.
As thiamazole is a suspected human teratogen, women of child-bearing age and
pregnant women should wear gloves when handling litter of treated cats.
Pregnant women should wear gloves when handling the veterinary medicinal product.
Special precautions for the protection of the environment:
Not applicable.

Concurrent treatment with phenobarbital may reduce the clinical efficacy of thiamazole.
Thiamazole is known to reduce the hepatic oxidation of benzimidazole wormers and
may lead to increases in their plasma concentrations when given concurrently.
Thiamazole is immunomodulatory, therefore this should be taken into account when
considering vaccination programmes.

Do not store above 25 ºC.
Tablet container: Keep the container tightly closed in order to protect from moisture.
Keep the container in the outer carton.
Blister: Keep the blister strips in the outer carton.

Not applicable.

This information is sourced from the official Summary of Product Characteristics (SPC) published by the Veterinary Medicines Directorate (VMD). It is provided for informational purposes only and does not replace professional veterinary advice. Always consult your vet before administering any medication.