Plan B One-Step is an emergency contraceptive containing levonorgestrel 1.5mg in a single-dose tablet. It is a backup method of birth control used after unprotected sex or contraceptive failure. Plan B One-Step works primarily by preventing or delaying ovulation and may also inhibit fertilization by altering tubal transport of sperm or ova. It is most effective when taken as soon as possible within 72 hours (3 days) after unprotected sex, with efficacy rates up to 89% when taken correctly as directed. The sooner it is taken, the more effective it becomes.

This product is available over-the-counter without a prescription and can be taken at any time during the menstrual cycle. Plan B One-Step is not for routine contraceptive use and will not work if pregnancy has already occurred. It does not affect an existing pregnancy and is not an abortion pill. It will not protect against HIV infection or other sexually transmitted diseases. Users should consult a healthcare provider before use if taking certain medications including efavirenz (HIV medication), rifampin (tuberculosis treatment), or seizure medications, as these can reduce effectiveness. Costco limits purchases to 2 units per membership.