There is no evidence that using Plan B once or multiple times causes infertility, according to Bedsider. This source also states that the greatest risk when using Plan B is unintended pregnancy as the pill is only effective in preventing seven out of eight pregnancies. Plan B is an emergency contraception pill that works by delaying ovulation so that the sperm and egg never have the opportunity to meet, Bedsider states.
RH Reality Check explains that Plan B is made up of progestin, the same hormone present in birth control pills and the female body. This source advises that using Plan B can cause irregular bleeding and can cause a woman's period to be either late or early, but it does not harm a pregnancy if one has already occurred. While Plan B is a valid safety net in the case of unprotected sex, RH Reality Check warns couples that it is not to be relied on as a regular form of birth control as it is much less effective than other methods of birth control. It is also more expensive.
Plan B is available over the counter without a prescription to women over the age of 17 at pharmacies, according to Bedsider. For women under 17, RH Reality Check advises that Plan B is available from pharmacies with a prescription.