How does BC work?
Answers: It does stop her from releasing an egg. As far as how effective it is, it depends on what type of birth control she is using. The shot (I am assuming Deprovera) is especially effective, 99% surrounded by fact. So that mode for every 100 women that take the shot, 1 would become pregnant. The just thing next to the shot is it does not protect against sexually transmitted diseases. So, for the most part you should not verbs that she will become pregnant, the shot is a very undamaging birth control method. :)
Here is a web site that explains how it works...
http://www.ciao.co.uk/Depo_Provera__Revi...
Hormonal contraceptives may be introduced into the woman’s body contained by many different ways, among them in words, vaginally, transdermally, or through injections or implants. The oral method be the first and most famous of these; inwardly a few years of its introduction in 1960, "the Pill" become one of the most popular contraceptives in the United States and elsewhere, and it remains so today.
Hormonal contraception may accomplishment in one or more ways to prevent pregnancy. It may lead to ovulation to cease, preventing the possibility of fertilization; it may thicken the woman’s cervical mucus, making permeation of the uterus by sperm more difficult; or it may alter and thin the endometrium so that a fertilized egg have difficulty implanting. (Technically, if the drug works surrounded by this third fashion, it act as a contragestive rather than a contraceptive, since it have not prevented conception, acting instead to prevent gestation.)