POM-V Prescription Required Companion Animal

Felimazole 5 mg/ml Oral Solution for Cats

Active ingredient: Thiamazole

Form

Liquid

Species

Cats

Manufacturer

Dechra Regulatory B.V.

VMD MA No.

50406/5036

What it's used for

For the stabilisation of hyperthyroidism prior to surgical thyroidectomy. 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 5 mg/ml Oral Solution for Cats — SPC Details

Source: VMD Summary of Product Characteristics (SPC). Last updated 26 Mar 2026.

For the stabilisation of hyperthyroidism prior to surgical thyroidectomy.
For the long-term treatment of feline hyperthyroidism.

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 pregnant or lactating females.
Do not use in cases of hypersensitivity to the active substance or to any of the
excipients.
Please refer to section 4.7.

Revised: April 2025
AN: 04388/2024

Adverse reactions 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 and, in these cases, treatment should be
stopped immediately and alternative therapy considered, following a suitable
period for recovery.
Uncommon
(1 to 10 animals / 1,000
animals treated):
Vomiting
, Anorexia
, Inappetence
, Lethargy
Pruritus
1,2
, Excoriation
1,2
Prolonged bleeding
1,3,4
Icterus
1,4
, Hepatopathy
Eosinophilia
, Lymphocytosis
, Neutropenia
,
Lymphopenia
, Leucopenia
(slight),
Agranulocytosis
Thrombocytopenia
1,5,6
, Haemolytic anaemia
Rare (1 to 10 animals /
10,000 animals treated):
Autoimmune disorder (serum anti-nuclear
antibodies)
Very rare
(<1 animal / 10,000 animals
treated, including isolated
reports):
Lymphadenopathy
, Anaemia
1
These side-effects resolve within 7-45 days after cessation of thiamazole
therapy.
Severe and of the head and neck.
Sign of a bleeding diathesis.
Associated with hepatopathy.
Immunological side-effect.

Revised: April 2025
AN: 04388/2024
Occurs uncommonly as a haematological abnormality and rarely as an
immunological side effect.
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.

In order to enhance stabilisation of the hyperthyroid patient the same feeding
and dosing schedule should be used daily.

Special precautions for use in animals
•
required, animals should be monitored particularly carefully.
•
be subject to careful risk : benefit 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.
•
anaemia.
•
are febrile, should have a blood sample taken for routine haematology and
biochemistry.
•
/litre) should be treated with
prophylactic bactericidal antibacterial drugs and supportive therapy.
•
access to drinking water.
•
Special precautions to be taken by the person administering the veterinary
medicinal product to animals
•
milk, women of child-bearing age and lactating women must wear non-
permeable single use gloves when handling the veterinary medicinal product,
vomit or used litter of treated animals. If you are pregnant, think you may be
pregnant or are attempting to conceive, you should not administer the
veterinary medicinal product or handle the litter/vomit of treated cats.
•
contact. Do not handle this veterinary medicinal product if you are allergic to
thiamazole or one of the excipients. 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 insert or
the label to the physician.
•
skin and eye contact including hand-to-eye contact. In case of accidental skin
and/or eye contact, rinse exposed skin and/or eyes immediately with clean
running water. If irritation develops, seek medical advice immediately and
show the package insert or the label to the physician.
•
arthralgia (joint pain), pruritus (itching) and pancytopaenia (decrease in blood
cells and platelets). Avoid oral exposure including hand-to-mouth contact,
especially by children.

Revised: April 2025
AN: 04388/2024
•
•
•
treated animals.
•
vomit or used litter of treated animals.
•
veterinary medicinal product remaining on the tip of the dosing syringe should
be wiped off with a tissue. The contaminated tissue should be immediately
disposed of. The used syringe should be stored with the veterinary medicinal
product in the original carton.
•
show the package insert or the label to the physician.
•
Special precautions for the protection of the environment
Not applicable.
Other precautions
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.

This veterinary medicinal product does not require any special storage
conditions.

Not applicable.
5.

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.