Overview

This is a study to assess the efficacy, safety, and tolerability of IMVT-1402 in adult participants with Graves' disease (GD) who are hyperthyroid despite antithyroid drug (ATD) treatment.

The primary objective of this study is to evaluate the efficacy of IMVT-1402 versus placebo as assessed by T3 (total triiodothyronine [T3] or free triiodothyronine [FT3]), free thyroxine (FT4), thyroid-stimulating hormone (TSH), and ATD dose at Week 26.

Eligibility

Inclusion Criteria:

• Have documented diagnosis of GD.
• Have a TSH value < 0.1 mIU/L as assessed by the local laboratory at the Screening Visit.
• Meet one of the following at the Screening Visit:
  • Have been on ATD for ≥ 3 months in the period immediately preceding the Screening Visit and both of the following:
    • Are on ATD at the Screening Visit with an ATD dose of ≥ 20 mg/day methimazole or equivalent for the 4-week period immediately preceding the Screening Visit.
    • Are anticipated to be on a stable dose of ATD for the 4-week period immediately preceding Randomization.
  • Have been on ATD for ≥ 6 months in the period immediately preceding the

    Screening Visit and all of the following:

    • Have been treated with ≥ 15 mg/day methimazole or equivalent at any point during the participant's treatment history.
    • Are on ATD at the Screening Visit with an ATD dose a specified amount of methimazole or equivalent for the 4-week period immediately preceding the Screening Visit.
    • Are anticipated to be on a stable dose of ATD for the 4-week period immediately preceding Randomization.

Additional inclusion criteria are defined in the protocol.

Exclusion Criteria:

• Have previously been treated with radioactive iodine (RAI) therapy or have undergone total thyroidectomy.
• Have a T3 (Total T3 or FT3, as available and per standard of care at local laboratory) or FT4 value < lower limit of normal (LLN) as assessed by the local laboratory at the Screening Visit.
• Have received levothyroxine, desiccated thyroid extract, or T3 at any dose within 6 weeks of the Screening Visit.
• Have a history of hyperthyroidism not caused by GD (e.g., toxic adenoma or toxic multinodular goiter) and/or history of thyroid storm within 6 months of the Screening Visit.
• Have an autoimmune disease other than GD requiring treatment that, in the Investigator's judgment, puts the participant at undue risk.
• Have moderate-to-severe active thyroid eye disease (TED) and are expected to require immediate surgical intervention and/or are planning corrective surgery/irradiation or medical therapy for TED during study participation.

Additional exclusion criteria are defined in the protocol.