The morning-after pill is most effective when taken as soon as possible after unprotected intercourse, ideally within 24 hours, though effectiveness varies by type and timing. Levonorgestrel-based pills (Plan B One-Step, Next Choice) are available over-the-counter and work best within 72 hours of intercourse, with some effectiveness up to 120 hours (5 days). Ulipristal acetate (ella) is a prescription medication that remains effective for up to 120 hours and may work better than levonorgestrel between 72–120 hours. The sooner any emergency contraceptive is taken, the higher the success rate at preventing pregnancy. Effectiveness decreases with time, so delaying use reduces the likelihood of preventing pregnancy. It's important to note that emergency contraception prevents pregnancy from occurring—it does not terminate an existing pregnancy. These pills work primarily by delaying or preventing ovulation. They are most reliable when taken before ovulation has occurred, which is why timing matters significantly. Factors like body weight and certain medications can affect levonorgestrel's effectiveness. If vomiting occurs within 2 hours of taking the pill, medical advice should be sought about whether a second dose is needed. Emergency contraception is not intended as a regular birth control method but rather as a backup option following unprotected intercourse, contraceptive failure, or other circumstances where pregnancy prevention is needed urgently.