Levothyroxine

Levothyroxine (also written L-thyroxine or LT4) is a synthetic version of the thyroid hormone thyroxine (T4). It is the standard treatment for hypothyroidism and for people who have had their thyroid removed or ablated with radioactive iodine.

Taken as a once-daily tablet, levothyroxine is absorbed in the gut and circulates in the blood. The body converts it to the more active T3 as needed. The dose is adjusted based on TSH and free T4 blood tests until hormone levels sit within the reference range.

Levothyroxine absorption is affected by several things. It should be taken on an empty stomach, ideally 30 - 60 minutes before food, coffee, or milk. Calcium and iron supplements and some antacids significantly reduce absorption if taken at the same time - leave a gap of at least four hours between these and levothyroxine. Soya and coffee can also reduce absorption. Proton pump inhibitors (PPIs) can affect absorption by changing stomach acidity, which a timing gap does not fix - if you take one regularly, your levels may need rechecking. Check with your pharmacist for your specific medicines.

Symptoms of under-treatment (feeling hypothyroid) or over-treatment (palpitations, anxiety, weight loss, poor sleep) should be discussed with your GP or specialist, who will check your blood levels.