October 5, 2015
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"The U.S. Food and Drug Administration today granted approval to Lenvima (lenvatinib) to treat patients with progressive, differentiated thyroid cancer (DTC) whose disease progressed despite receiving radioactive iodine therapy (radioactive iodine"...


(levothyroxine sodium)



  • Thyroid hormones, including TIROSINT, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss.
  • In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction.
  • Larger doses may produce serious or even life threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects [See ADVERSE REACTIONS, DRUG INTERACTIONS, and OVERDOSAGE].


TIROSINT (levothyroxine sodium) is L-thyroxine. The orally administered gelatin capsules contain synthetic L-3,3',5,5'-tetraiodothyronine sodium salt [levothyroxine (T4) sodium]. Synthetic T4 is chemically identical to that produced in the human thyroid gland. Levothyroxine (T4) sodium has an empirical formula of C15H10I4NNaO4 • x H2O (where x = 5), molecular weight of 798.86 g/mol (anhydrous), and structural formula as shown:

TIROSINT (levothyroxine sodium) Structural Formula Illustration

The inactive ingredients in TIROSINT are gelatin, glycerin and water.

What are the possible side effects of levothyroxine (Levothroid, Levoxyl, Synthroid, Tirosint, Unithroid)?

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have a serious side effect such as:

  • headache;
  • sleep problems (insomnia);
  • feeling nervous or irritable;
  • fever, hot flashes, sweating;
  • pounding heartbeats or fluttering in your chest;
  • changes in your menstrual periods; or
  • appetite changes, weight changes.

Less serious side...

Read All Potential Side Effects and See Pictures of Tirosint »

Last reviewed on RxList: 3/14/2012
This monograph has been modified to include the generic and brand name in many instances.

Report Problems to the Food and Drug Administration


You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

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