The morning after pill, or emergency contraception is designed to use when a woman has unprotected sex or her regular method of contraception fails. Emergency contraception can be taken up to five days after unprotected intercourse however, the sooner it is taken after unprotected sex the better chance it has of successfully preventing a pregnancy. If taken within the first 24 hours, it has a 95% success rate.
While there are no reported harmful effects of long term use, emergency contraception is not designed for a woman to use as her primary method of contraception. While a woman can take the morning after pill as many times as she likes or needs, repeated use of emergency contraception may cause a woman to have irregular bleeding and cause changes to her menstrual cycle altogether. Changes may include the length of the menstrual cycle increasing or decreasing and periods being lighter or heavier than before.
Also, using the morning after pill repeatedly is not cost effective as other methods of contraception are less expensive on the whole. Further, while the morning after pill has a 95% success rate if taken within 24 hours after unprotected sex, other methods of contraception are more reliable. The pill for example has a 99% success rate for prevention of pregnancy, the IUD has a 99.9% success rate and condoms used with spermicide have a 98% success rate.
Side effects associated with emergency contraception such as nausea and vomiting are also something to consider with repeated use. If a woman experiences these side effects the first time she uses emergency contraception, it is likely she will experience them each time. Whereas consistent use of another method of contraception will not disrupt the body like the morning after pill.
Lastly, while there are no limits to how many times a woman can take the morning after pill, it is important to keep in mind that it is designed as a back up emergency method of contraception and does not provide ongoing protection against pregnancy.