Liothyronine use in a 17 year observational population-based study - the tears study

To look at adverse outcomes for patients on liothyronine compared to l-thyroxine. Some trials have examined the relative merits of liothyronine but none have looked at adverse outcomes in large numbers.

An observational study of all patients prescribed thyroid hormone replacement in Tayside Scotland (population 400 000) from 1997 to 2014.

A study group of patients having ever used liothyronine (n = 400) was compared to those who had only used l-thyroxine (n = 33 955). All patients were followed up until end-point, death or leaving Tayside.

Mortality rates and admissions with cardiovascular disease, atrial fibrillation, fractures, breast cancer and mental diseases were compared. Incident use of bisphosphonates, statins, antidepressants and antipsychotics was compared.

Compared to patients only taking l-thyroxine, those using liothyronine had no increased risk of cardiovascular disease [hazard ratio (HR) 1·04; 95% CI 0·70-1·54], atrial fibrillation (HR 0·91: 0·47-1·75), or fractures (HR 0·79: 0·49-1·27) after adjusting for age. There was no difference in the number of prescriptions for bisphosphonates or statins. There was an increased risk of new prescriptions for antipsychotic medication (HR 2·26: 1·64-3·11 P < 0·0001) which was proportional to the number of liothyronine prescriptions. There was a non-significant trend towards an increase in breast cancer and new use of antidepressant medications. During follow-up, median TSH was higher for patients on l-thyroxine alone (2·08 vs 1·07 mU/L; P < 0·001).

For patients taking long-term liothyronine we did not identify any additional risk of atrial fibrillation, cardiovascular disease or fractures. There was an increased incident use of antipsychotic medication during follow-up.