Desiccated thyroid (Armour Thyroid) and levothyroxine (Euthyrox) are both prescription medications used to treat hypothyroidism, a condition where your thyroid doesn't produce enough hormones. But they have some important differences. Desiccated thyroid is a natural thyroid hormone replacement that contains both T3 and T4 hormones, is derived from animal sources, and is taken once daily. In contrast, levothyroxine is a synthetic form of the T4 hormone and is also taken once daily, typically 30 minutes before breakfast. Armour Thyroid is not approved by the FDA, whereas levothyroxine is a first-choice, FDA-approved treatment for hypothyroidism. Side effects of both medications are typically related to having too much thyroid hormone and include headache, restlessness, and trouble sleeping. Both medications require careful management of drug interactions. Levothyroxine is available as a lower-cost generic, whereas desiccated thyroid only comes as a branded medication.