Addition of lithium carbonate to carbamazepine: hematological and thyroid effects

In view of the increasing use of lithium-carbamazepine combination therapy for refractory psychiatric disorders, the authors assessed the clinical laboratory effects of adding lithium to carbamazepine in 23 patients with affective disorders. Lithium produced a robust reversal of carbamazepine-induced leukopenia, increasing WBCs, predominantly neutrophils, to levels significantly above placebo baseline values. The combination produced additive antithyroidal effects, resulting in greater decreases in T4 and free T4 than with carbamazepine alone; the addition of lithium was associated with the emergence of a modestly higher TSH level. The authors discuss clinical and theoretical implications of these findings.