Sinemet and thyroid function in Parkinson disease.

Patients on chronic carbidopa-levodopa (Sinemet) therapy underwent thyroid function testing that included measurement of serum thyroxine (T4), triiodothyronine (t3), thyrotropin (TSH), T3 uptake (T3U), free T4 index (FT4I), and free T3 index (FT3I). The subjects were studied both in a random sampling and in a controlled manner, fasting and 2 hours after receiving the drug. All subjects were euthyroid by testing, and there was no significant difference in thyroid hormone levels of patients and controls or in fasting values and values 2 hours after the drug. However, there was a small but significant reduction in serum TSH levels after Sinemet. Therapeutic doses of Sinemet have no significant effect on thyroid function in euthyroid patients with Parkinson disease.