LEVOTHYROXINE SODIUM IS A SYNTHETIC THYROID HORMONE THAT INCREASES CELLULAR METABOLISM AND PLAYS AN IMPORTANT ROLE IN GROWTH,DEVELOPMENT, CNS AND BONE FUNCTIONS, FOOD METABOLISM AND BODY TEMPARATURE.THYROID HORMONES,T&T ARE THOUGHTTO ACT BY BINDING TO THYROID RECEPTOR PROTEINS ATTACHED TO DNA,THUS ACTIVATING GENE TRANSCRIPTION AND PROTEIN SYNTHESIS. THE PHYSIOLOGICAL ACTIVITIES OF THYROID HORMONES ARE PRODUCED PRIMARILY BY T AND APPROXIMATELY 80% OF T IS DERIVED FROM T4 BY DEIODINATION IN PERIPHERAL TISSUES.