POM-V Prescription Required Companion Animal

Thyronorm 5 mg/ml Oral Solution for Cats

Active ingredient: Thiamazole

Form

Liquid

Species

Cats

Manufacturer

VIRBAC

VMD MA No.

05653/3064

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

Thyronorm 5 mg/ml Oral Solution for Cats — SPC Details

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

For the long-term treatment of feline hyperthyroidism.

The veterinary medicinal product should be administered directly into the mouth of
the cat using the measuring syringe. The syringe is graduated in 0.5 mg up to 5 mg.
Do not administer in food as efficacy of the veterinary medicinal product when
administered via this route has not been established.
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 of thiamazole (1 ml of the product) per day.
The total daily dose should be divided into two and administered morning and
evening. If, for reasons of compliance, once daily dosing is preferable, then this is
acceptable, although a 2.5mg dose (=0.5ml of the product) given twice daily may be
more efficacious in the short term. In order to enhance stabilisation of the
hyperthyroid patient the same dosing schedule relative to feeding should be used
daily.
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.
Standard dose adjustments should be made in increments of 2.5 mg of thiamazole
(0.5 ml of the product) and the aim should be to achieve the lowest possible dose
rate. In cats that require particularly small dose adjustments, increments of 1.25 mg
of thiamazole (0.25 ml of the product) can be used. If total T4 concentration drops
below the lower end of the reference interval, and particularly if the cat is showing
clinical signs of iatrogenic hypothyroidism (e.g. lethargy, inappetence, weight gain
and/or dermatological signs such as alopecia and dry skin), consideration should be
given to reducing the daily dosage and/or dosing frequency.
If more than 10 mg of thiamazole per day is required animals should be monitored
particularly carefully.
The dose administered should not exceed 20 mg of thiamazole per day.
For long-term treatment of hyperthyroidism, the animal should be treated for life.

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. Please refer to section 3.7.
Do not use in cases of hypersensitivity to the active substance or to any of the
excipients.

Cats:
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)
5,7
.
Very rare
(<1 animal / 10,000 animals
treated, including isolated
reports):
Lymphadenopathy
5,7
, Anaemia
5,7
.
Resolves 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.
Occurs uncommonly as a haematological abnormality and rarely as an
immunological side effect.
Treatment should be stopped immediately and alternative therapy considered
following a suitable period for recovery.
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.
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 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 safe use in the target species:
If more than 10 mg of thiamazole 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 renal
impairment may occur.
Haematology must be monitored due to risk of leucopenia or haemolytic anaemia
before initiating treatment and closely afterwards.
Any animal that suddenly appears unwell during therapy, particularly if it is 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.
Please refer to section 3.9 for monitoring instructions.
As thiamazole can cause haemoconcentration, cats should always have access to
drinking water.
In hyperthyroid cats, gastrointestinal disorders are common and may interfere with
the success of the oral therapy.
Special precautions to be taken by the person administering the veterinary medicinal
product to animals:
People with known hypersensitivity (allergy) to thiamazole or one of the excipients
should avoid contact with the veterinary medicinal product. 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 label to the physician.
This veterinary medicinal product may cause skin or eye irritation. Avoid eye contact
including hand to eye contact. In case of accidental eye contact, rinse eyes
immediately with clean running water. If irritation develops, seek medical advice.
Wash hands with soap and water after administration of the veterinary medicinal
product and handling the vomit of or litter used by treated animals. Wash any
spillages or spatter from skin immediately. Thiamazole may cause gastrointestinal
disturbances, headache, fever, joint pain, pruritus (itching) and pancytopaenia
(decrease in blood cells and platelets).
Avoid dermal and oral exposure, including hand-to-mouth contact.
Do not eat, drink or smoke while handling the product or used litter.
In case of accidental ingestion, seek medical advice immediately and show the
package leaflet or the label to the physician.
Following administration of the product any residual veterinary medicinal product
remaining on the tip of the dosing syringe should be wiped clean with a tissue. The
contaminated tissue should be immediately disposed of.
The used syringe should be stored with the product in the original carton.
As thiamazole is a suspected human teratogen, women of child-bearing age
must wear non-permeable single-use gloves when administering the veterinary
medicinal product or handling the litter/vomit of treated cats.
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.
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.

Keep the container tightly closed.
This veterinary medicinal product does not require any special temperature storage
conditions.

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.