POM-V Prescription Required Companion Animal

Thyrasol 5 mg/ml, Oral Solution for Cats

Active ingredient: Thiamazole

Form

Liquid

Species

Cats

Manufacturer

CP Pharma Handelsgesellschaft mbH

VMD MA No.

20916/5004

What it's used for

For the stabilisation of hyperthyroidism in cats 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

Thyrasol 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 in cats prior to surgical thyroidectomy.
For the long-term treatment of feline hyperthyroidism.

Oral use.
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 (= 1 mL of the product) per day.
Wherever possible, the total daily dose should be divided into two and administered
morning and evening.
The dose should be administered directly in the mouth using the syringe.
If, for reasons of compliance, once daily dosing is preferable, then this is acceptable
although a 2.5 mg dose (= 0.5 mL of the product) given twice daily may be more
efficacious in the short term.
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 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.

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 cases of hypersensitivity to the active substance or to any of the
excipients.
Do not use during pregnancy or lactation. Please refer to section 4.7.

Revised June 2024
AN: 02930/2023

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.
Adverse reactions are uncommon. The most common clinical side effects that are
reported include vomiting, inappetance/anorexia, weight-loss, lethargy, severe
pruritus and excoriations of the head and neck, bleeding diathesis and icterus
associated with hepatopathy, and haematological abnormalities (eosinophilia,
lymphocytosis, neutropenia, lymphopenia, slight leucopenia, agranulocytosis,
thrombocytopenia or haemolytic anaemia). These side effects resolve within 7-45
days after cessation of thiamazole therapy.
Possible immunological side effects include anaemia, with rare side effects including
thrombocytopenia and serum anti-nuclear antibodies, and, very rarely,
lymphadenopathy can occur. Treatment should be stopped immediately and
alternative therapy considered following a suitable period for recovery.
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.
The frequency of adverse reactions is defined using the following convention:
very common (more than 1 in 10 animals treated- displaying adverse reaction(s))
common (more than 1 but less than 10 animals in 100 animals treated)
uncommon (more than 1 but less than 10 animals in 1,000 animals treated)
rare (more than 1 but less than 10 animals in 10,000 animals treated)
very rare (less than 1 animal in 10,000 animals treated, including isolated reports).

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
If more than 10 mg of thiamazole per day is required animals should be monitored
particularly carefully.
As thiamazole can cause haemoconcentration, cats should always have access to
drinking water.
Use of the 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.
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, if needed
according to the benefit/risk assessment of the prescribing veterinarian.
Please refer to section 4.9 for monitoring instructions.
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 doctor.
This product may cause skin and/or eye irritation. Avoid skin and eye contact
including hand to eye contact.
In case of accidental skin and/or eye contact, rinse skin and/or eyes immediately with
clean running water. If irritation develops, seek medical advice.
Wash hands with soap and water after administration of the product and handling the
vomit of or litter used by treated animals.
Thiamazole may cause gastrointestinal disturbances, headache, fever, joint pain,
pruritus (itching) and pancytopaenia (decrease in blood cells and platelets).
Avoid 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.
Do not leave filled syringes unattended.
Following administration of the product any residual 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.

Revised June 2024
AN: 02930/2023
As thiamazole is a suspected human teratogen, women of child-bearing age must
wear non-permeable single-use gloves when administering the 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 product or handle the litter/vomit of treated cats.

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.

Revised June 2024
AN: 02930/2023

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

Excipients:
Sodium benzoate (E211) 1.5 mg
For the full list of excipients, see section

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.