Levothyroxine, and how to take it

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Levothyroxine is a man-made version of T4, the hormone the thyroid makes. It replaces the thyroxine an underactive thyroid can’t make enough of, and, like the thyroid’s own T4, the body turns it into T3, the form it uses.

The dose depends on body weight and blood test results. As levels rise, the pituitary sends less TSH. It’s usually taken every day, for life.

Levothyroxine is best taken:

• In the morning with water, on an empty stomach
• At least 30 minutes before food or other drinks
• At least 4 hours apart from calcium, iron, some cholesterol medicines and multivitamins

Tea and coffee count: wait at least 30 minutes before a drink with caffeine.

If you forget the occasional dose, take it as soon as you remember. The body holds a big reserve, so one missed dose won’t make an immediate difference.

Missing doses regularly can make blood tests look as if the dose is wrong.

Levothyroxine is slow-acting, so it may take several months for symptoms to ease.

Blood tests aren’t usually done until 3 months after starting or changing a dose, because levels are still settling.

On levothyroxine, guidance for doctors is to check TSH every 3 months until it’s steady (2 similar results in range, 3 months apart), then once a year.

On levothyroxine, the aim is to keep TSH within the lab’s range, without doses so high they push TSH right down.

Pharmacies don’t always give the same brand, and most people notice no difference. If you feel less well on a certain brand, talk to your doctor.

Sources: British Thyroid Foundation: hypothyroidism; British Thyroid Foundation: your thyroid gland; British Thyroid Foundation: thyroid function tests; British Thyroid Foundation: living with hypothyroidism; NICE NG145