Study to Evaluate Serum Free Thyroxine (FT4) and Free Triiodothyronine (FT3) Measurements for Subjects Treated With Eslicarbazeine Acetate (ESL)

The purpose of this research study is to determine if the blood tests used to measure free thyroid hormone levels are affected by a drug called eslicarbazepine acetate. To determine if eslicarbazepine acetate interferes with these blood tests, blood samples will be analysed so that researchers can compare different types of lab tests that measure these thyroid hormones. Half of the people who participate in this study will already be taking eslicarbazepine acetate either as a study drug or as a prescription (Part 1) and the other half will be people who do not take eslicarbazepine acetate (Part 2).