During the start of the replacement therapy with levothyroxine, blood tests are usually performed every six to eight weeks to help adjust doses. Infants and children are usually started on full levothyroxine replacement doses and the frequency of blood tests, growth and intellectual development is age-dependent.

Side effects from levothyroxine are usually due to over-dosage and include nervousness, weight loss, tachycardia (rapid heart beat), irritability, and anxiety.

August 14, 1997 Federal Register, FDA announced that orally administered drug products containing levothyroxine sodium are new drugs. In all actuality levothyroxine products have been sold since the 1950's.  But they stated that "The unapproved thyroid hormone replacement products that have been on the market have been associated with stability and potency problems. These problems have resulted in product recalls and have the potential to cause serious health consequences to the public."

Finally four years later, the agency announced that any orally administered levothyroxine drug product must be the subject of an approved New Drug Application. If there is no such approved application, the product will be subject to regulatory action as an unapproved new drug. With the approval today of Unithroid, patients and physicians now have available to them an oral levothryroxine sodium drug product that has been determined to be safe and effective by the FDA and that also meets FDA standards for manufacturing.