Levolet is for use alone or in combination with antithyroid agents to treat hypothyroidism, goiter, chronic lymphocytic thyroiditis, myxedema coma, and stupor.

Levolet acts like the endogenous thyroid hormone thyroxine (T4, a tetra-iodinated tyrosine derivative). In the liver and kidney, T4 is converted to T3, the active metabolite. In order to increase solubility, the thyroid hormones attach to thyroid hormone binding proteins, thyroxin-binding globulin, and thyroxin-binding prealbumin (transthyretin). Transport and binding to thyroid hormone receptors in the cytoplasm and nucleus then takes place. Thus by acting as a replacement for natural thyroxine, symptoms of thyroxine deficiency are relieved.

Currently there are no known off label uses for Levolet.

Levolet or levothyroxine is taken on an empty stomach approximately half an hour to an hour before meals to maximize its absorption, often with water to ease swallowing and help the tablet dissolve for absorption.

There are also foods and other substances that can interfere with absorption of thyroxine replacement. Patients under treatment ought to avoid taking calcium and iron supplements within 4 hours, as well as soy products within 3 hours of taking the medication, as these can reduce absorption of the drug. Other substances that reduce absorption are aluminium and magnesium containing antacids, simethicone or sucralfate, cholestyramine, colestipol, Kayexalate. Recently, it has been discovered that caffeine may also interfere with the intestinal absorption of levothyroxine.

Different substances cause other adverse effects that may be severe. Ketamine may cause hypertension and tachycardia and tricyclic and tetracyclic antidepressants increase its toxicity. On the other hand Lithium can cause hyperthyroidism (but most often hypothyroidism) by affecting iodine metabolism of the thyroid itself and thus inhibits synthetic levothyroxine as well.