Displaying 31 results of Levothyroxine Impurities Levothyroxine is a synthetic form of the thyroid hormone used to treat hypothyroidism. However, during the manufacturing process, impurities can be introduced that affect the quality and efficacy of the medication. These impurities can include degradation products, residual solvents, and heavy metals. It is important to monitor and control the levels of these impurities to ensure the safety and effectiveness of the medication for patients.