Inclusion Criteria:

• Diagnosed with primary hypothyroidism, including Hashimoto's Thyroiditis, and on therapy with a stable dose of LT4 (minimum 50 mcg per day, administered 7 days per week) for at least 12 weeks prior to Screening
• Have had euthyroid status for at least 6 weeks and up to 12 months prior to Screening (Visit 1), with at least one documented minimum stable dose of 50 mcg LT4.
• 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
• Hospitalization for a major illness within 5 weeks prior to Screening
• Concomitant use of prohibited medications or supplements
• Have uncontrolled diabetes
• Taking or having taken prescription or over-the-counter weight loss medications within 6 weeks prior to Screening
• 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