Plan B is an emergency contraceptive medication used to prevent pregnancy after unprotected intercourse. Its active ingredient levonorgestrel is a synthetic progestin that works by inhibiting ovulation and altering the uterine lining. The drug influences the endocrine system by binding to progesterone receptors and suppressing the luteinizing hormone surge required for egg release. It also reduces sperm motility and fertilisation capacity within the reproductive tract. By modifying the endometrium the medication creates an environment less suitable for implantation should fertilisation occur. The therapeutic effect relies on timely administration within the first few days after intercourse to maximize efficacy.

Plan B is an emergency contraceptive that prevents pregnancy after unprotected sexual intercourse. It contains the synthetic hormone levonorgestrel which acts primarily to inhibit ovulation. By blocking the release of an egg from the ovary the drug stops fertilization from occurring. If ovulation has already taken place the medication may also alter the uterine lining to reduce the chance of implantation. These actions are achieved through selective binding to progesterone receptors that regulate reproductive hormones. The resulting hormonal changes prevent the formation of a viable zygote and therefore avoid pregnancy. The overall effect is a single intervention that rapidly reduces the likelihood of conception within the first few days after exposure.

Headache often occurs after taking the medication. Nausea may be experienced by some users. Drowsiness can affect daily activities. Dry mouth is a frequent complaint. Fatigue may be noted in certain individuals. Dizziness sometimes accompanies the treatment. Skin rash can develop in rare cases.

Headache is frequently reported among users of oral contraceptives. Nausea often occurs shortly after taking the medication. Fatigue can be experienced during the first few days of use. Some individuals notice mild dizziness when standing up quickly. Skin reactions such as rash may appear in rare cases. Weight changes are occasionally noted but not consistently observed. Overall these effects tend to be temporary and vary between individuals.