Medication blocks the production of thyroxine by the thyroid gland. It comes in tablet or liquid form and needs to be given every day for life, normally twice a day. Blood samples need to be checked periodically to ensure that thyroid levels are within the normal range. If they’re not, the dosage will need to be adjusted. Your vet will need to check your cat regularly to see how they are doing on the medication.  

Advantages of medication: 

• relatively cheap for each prescription, and costs are spread over a longer period 
• simple  
• no surgery or hospitalisation required 
• it can be stopped or adjusted 

Disadvantages of medication: 

• not a permanent cure as medication must be given for life 
• some cats can be difficult to medicate 
• can produce side effects, including poor appetite, vomiting, skin reactions or liver disease 
• periodic blood tests will be required to monitor the condition, and dose adjustments may be needed 
• the combination of monitoring and longer-term medication can become costly 

Surgery involves removing one or both of the thyroid glands under general anaesthesia. Before surgery, cats will often need medication to stabilise the condition.  

Advantages of surgery: 

• successful surgery is a permanent cure  
• the one-off cost may be cheaper in the long term than medication 
• a specialist centre is not normally required to perform the procedure 
• prolonged hospital stays are not normally required 

Disadvantages of surgery: 

• if one gland is affected and removed, the other side may become affected at a later date, causing symptoms to recur. Both sides may be removed to prevent this 
• in cases where a cancerous tumour is present in the thyroid, it can be difficult to remove completely 
• a small percentage of hyperthyroid cats may have thyroid tissue that’s out of reach (known as ‘ectopic’ tissue). They will remain hyperthyroid after removal of the thyroid glands in the neck 
• small glands next to the thyroid called parathyroid glands help control calcium levels in the body. These can sometimes be damaged during surgery, causing levels of calcium to drop, which can be life-threatening 
• surgery requires a general anaesthetic and may not be suitable for cats with other ongoing problems 

Radioactive iodine is injected under the skin to destroy the abnormal thyroid tissue, leaving normal cells unaffected. 

Advantages of radiation: 

• no anaesthetic is required 
• usually cured completely with a single treatment 
• it can be a good alternative to surgery if a cancerous tumour is present on the thyroid 

Disadvantages of radiation: 

• cannot be performed routinely at local practices. Specialist centres are required 
• requires hospitalisation and complete isolation usually for around one to two weeks. The cat cannot be handled during this time due to the radiation levels in the body 
• it’s more expensive initially than medication, but may be cheaper in the long term 
• may cause levels of thyroxine to be too low after treatment, which will occasionally need medication 

A special low-iodine diet can help control thyroid hormone levels. This can be prescribed by your vet. 

This diet must be your cat’s only source of food. If they eat other food, including prey, the diet won’t be effective.  

The long-term effects of feeding a low-iodine diet to cats are currently uncertain. 

What not to feed a cat with hyperthyroidism 

Foods that are high in iodine can make hyperthyroidism worse. These include: 

• fish 
• fish oils 
• seaweed