The North Star study is a multi-center, Phase 2, double-blind, randomized, parallel group clinical study to evaluate the safe and effective dose conversion from Levothyroxine to North Star therapy.

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