During your menstrual cycle, many hormones are released – starting a chain reaction. The pituitary gland in the brain releases FSH which stimulates the growth of follicles and a premature egg in the ovaries. These follicles then release estrogen which helps prepare the uterus lining and triggers the brain to release luteinizing hormone (LH). LH then triggers ovulation in which the egg is released into the fallopian tubes where it spends around twelve to twenty-four hours waiting to be fertilized. If the egg isn’t fertilized in this time it begins to dissolve and is shed away with the uterine lining during menstruation.

Though this window of opportunity is brief, it’s increased by the fact that sperm can live for up to five days – showing up early awaiting ovulation.

Regular daily birth control pills modify these hormone levels. By increasing progestin levels, your body thinks it has already released an egg or that its already pregnant. It effectively decreases FSH and LH and then the cycle halts.

But in the case of the Morning After emergency contraceptive pill which is taken after sex, a few different mechanisms take place.

Morning After works because fertilization doesn’t happen immediately or even within hours immediately after sex. Instead the sperm must undergo a few biological changes in the fallopian tube first – which takes time! This is why Morning After works up to three days after sex – the sooner you take it, the more effective it is.

If taken during the first half of the menstrual cycle, Morning After works specifically to prevent ovulation – the egg is not released, even though it may be ready, the sperm cannot fertilize it.

In cases where it’s too late to prevent ovulation, emergency contraception is believed to also thicken cervical mucus and trap sperm. It may also directly inhibit fertilization between sperm and egg.

Morning After prevents pregnancy. It is unable to cause an abortion. In fact, it will not even harm an existing pregnancy.

Levonorgestrel, the active ingredient in Morning After, has been used in regular birth control pills for decades. Scientific studies have demonstrated its safety in women of all ages. While some minor side effects may occur such as nausea or vomiting, the benefits far outweigh the risks.

Morning After is available over-the-counter without a prescription or ID. It’s approved for women of all ages and can be found in the family planning or feminine care isle at drug stores.