Euthyrox 100mcg is a prescription medication containing levothyroxine sodium, manufactured by Merck. This medication comes in a package of 100 tablets, with each tablet containing 100 micrograms of the active ingredient. Euthyrox contains levothyroxine sodium, which is a synthetic form of the thyroid hormone. The 100mcg strength indicates the dosage of levothyroxine in each tablet. As this is a prescription medication, it should only be taken under the supervision and direction of a healthcare provider.