The contraceptive shot (or birth control injection) is a method of contraception whereby the hormone progestogen is injected into the muscle every third month. It works the same as mini pills; the cervical mucus gets thicker which blocks sperm cells from getting to the egg. It also makes it more difficult for a fertilised egg to attach itself to the lining of the womb. The shot can sometimes, but not always, stop ovulation. This means that there is a chance that an egg cell might get fertilised and then be rejected from the womb as it cannot attach itself to the lining of the womb. There are other disadvantages with the shot: the woman might get irregular periods and it increases the risk of osteoporosis.