Levonorgestrel (LNG)

Levonorgestrel is a second generation synthetic progestogen used as an active ingredient in some hormonal contraceptives, including combined oral contraceptive pills, progestogen only pills, emergency contraceptive pills, intrauterine systems, contraceptive implants, and hormone replacement therapy. Levonorgestrel is used in emergency contraceptive pills (ECPs), both in a combined Yuzpe regimen which includes estrogen, and as a levonorgestrel-only method. The levonorgestrel-only method uses levonorgestrel 1.5 mg (as a single dose or as two .75 mg doses 12 hours apart) taken within 3 days of unprotected sex, with one study indicating that beginning as late as 120 hours after intercourse could be effective. If taken together with drugs that induce the CYP3A4 cytochrome liver enzyme, the levonorgestrel will be metabolized faster and have lower efficacy, and a larger dose will be needed.