So your cat’s been diagnosed, they’re on methimazole or carbimazole, and your vet has started talking about next steps. The medication is doing its job for now – but it’s not a cure, and most owners eventually want something more permanent.

Here’s how the treatment options compare.

Daily medication

Most cats that are newly diagnosed with hyperthyroidism are started on daily medication. This is administered either via tablets or transdermally (onto the skin).

It’s worth remembering: long-term medication means twice-daily dosing, blood tests every few months, and the possibility of side effects.

Radioiodine — the ‘gold standard’

There’s a reason radioiodine gets called the gold standard, and it’s not just marketing. A single injection of iodine-131 seeks out the overactive thyroid tissue and destroys it. Healthy tissue is left alone. No general anaesthetic, no surgical wound, and cure rates between 95% and 99%.

Your cat will need to remain at the hospital for a period of time, usually between two days and two weeks, until some of the iodine has cleared from their system, and you will then need to follow certain restrictions at home for another two weeks, such as keeping your cat in a separate room and disposing of their litter under strict conditions.

Expect to pay somewhere between £3000 and £4000. That usually covers the injection and hospital stay, but blood work and follow-up appointments are often billed separately. Your vet will need to submit a referral, and the centre will want recent bloods, blood pressure, and sometimes a heart scan before they’ll book your cat in.

Surgery

Removing the affected thyroid gland is a straightforward procedure and it can be curative. It tends to work best when only one gland is overactive. The most common complication is damage to the parathyroid glands – they sit right next to the thyroid and control calcium levels. If both thyroid glands need removing, the risk goes up. And even after a successful single-side surgery, the other gland can become a problem down the line. This surgery also requires a general anaesthetic, which is higher risk in hyperthyroid cats, which are often geriatric and have co-morbidities (other diseases as well as hyperthyroidism).

Low-iodine diet

Hill’s y/d is a prescription diet specifically formulated with a very low iodine content, because the thyroid gland needs iodine to produce thyroid hormones — by severely restricting iodine intake, we can reduce the amount of hormone the overactive thyroid gland is able to make. It works best when fed exclusively, meaning no other foods, treats, or flavoured medications, as even small amounts of iodine from other sources can undermine its effectiveness. Therefore it is only really appropriate for indoor only cats.

Where to get radioiodine treatment?

Only a handful of centres in the UK are licensed to offer radioiodine – speak to your vet about which centre is closest or most appropriate for your cat.