FDA Approves Gwyn Lo, First Once-Weekly Low-Dose Estrogen Birth Control Patch

The FDA has approved Viatris's Gwyn Lo, a new once-weekly low-dose estrogen birth control patch. Delivering norelgestromin and ethinyl estradiol, Gwyn Lo offers the lowest daily estrogen dose among available patches. In a phase 3 trial, Gwyn Lo demonstrated a Pearl Index of 4.14 for women aged 18-35 and showed strong adhesion, with only 1.3% of patches fully detaching. Gwyn Lo is approved for women with a BMI under 30, but is contraindicated for smokers over 35 due to cardiovascular risks.

Gwyn Lo FDA approval

• ▪The United States Food and Drug Administration approved Gwyn Lo, a once-weekly birth control patch developed by Viatris to prevent pregnancy.
• ▪Gwyn Lo is expected to become commercially available in the United States later in 2026.

Low-dose estrogen patch formulation

• ▪Gwyn Lo delivers 220 micrograms per day of norelgestromin and 20 micrograms per day of ethinyl estradiol directly through the skin.
• ▪Gwyn Lo provides the lowest daily dose of ethinyl estradiol among available contraceptive patches.
• ▪Gwyn Lo is applied once weekly for three consecutive weeks, followed by one patch-free week.

Phase 3 clinical trial results

• ▪The most common side effects of Gwyn Lo in trials included application-site irritation, redness, itching, intercycle bleeding, heavy withdrawal bleeding, and nausea.
• ▪The phase 3 clinical trial of Gwyn Lo measured contraceptive effectiveness using the Pearl Index, which reflects pregnancies per 100 woman-years.
• ▪Unscheduled bleeding or spotting among Gwyn Lo users decreased from 34.5% in the first cycle to 20% by cycle 13.
• ▪The Pearl Index for Gwyn Lo was 4.14 among women ages 18 to 35 during the phase 3 clinical trial.

Adhesion performance data

• ▪Only 1.3% of the 39,790 Gwyn Lo patches applied during the clinical trial fully detached.
• ▪Gwyn Lo demonstrated strong adhesion in real-world conditions during a year-long clinical trial.

BMI eligibility restrictions

• ▪Women with a body mass index of 30 or higher may experience an increased risk of blood clots when using Gwyn Lo.
• ▪Gwyn Lo is approved for women with a body mass index below 30 who are appropriate candidates for combined hormonal contraceptives.

Smoking contraindication for users

• ▪Women who smoke and are older than 35 should not use Gwyn Lo due to risks of heart and blood vessel complications.
• ▪Patients are advised to discuss their medical history and risk factors with a healthcare provider before using Gwyn Lo.

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