Serum total and free thyroid hormone concentrations were investigated in 126 patients with epilepsy taking anticonvulsants monotherapy (taking valproate: n=64, taking carbamazepine n=62) at least for one year to assess the long-term effects of antiepileptic drugs on thyroid hormone levels. Control group (n=21) was selected from healthy individuals who had the same age range.

Results indicated that mean T3 levels in valproate group were significantly higher than both carbamazepine and control groups (values were 1.81±1.72, 1.21±0.26, 1.32±0.24 ng/ml respectively p<0.05). There was also a significant difference in terms of FT3 levels between two monotherapy groups (values were 3.33±1.00 in valproate group; 3.83±1.01 pg/ml in carbamazepine group respectively p<0.05).

There was a weak positive correlation between serum TSH and valproate levels and a weak negative correlation between serum TSH and drug intake duration of carbamazepine therapy.

Since antiepileptic drugs may have diverse endocrine effects, in order to know the degree of these alterations, thyroid hormone measurements will provide additional informations before starting and monitoring therapeutic regimens on these patients.