A Study Evaluation the Safety and Efficacy of Hormone Replacement Therapy With North Star Compared to Levothyroxine in Patients With Primary Hypothyroidism

Inclusion Criteria: * Diagnosed with primary hypothyroidism * On continuous thyroid replacement therapy for at least 6 months before Study Entry * On a stable daily dose of LT4 for a minimum of 12 weeks prior to Screening * Agree to practice a method of contraception * Female patients not pregnant or lactating at Screening * Agree to practice a method of contraception of greater than 90% reliability * Willing to give written informed consent for the Study * Provide written authorization for use and disclosure of protected health information Exclusion Criteria: * Any clinical condition or previous surgery that might affect the absorption, distribution, biotransformation or excretion of North Star or levothyroxine * Hospitalization for a major illness within 4 weeks prior to Screening * Anticipated initiation or change in concomitant medications * Concomitant use of prohibited medications or supplements * Participated in another investigational new drug study within 30 days or 5 half-lives of the IMP, whichever is longer, prior to the first study drug administration. * For female subjects, be pregnant, nursing or planning to become pregnant during the study