Birth control injections that last for 13 to 15 weeks, at which time the woman has to get another Depo shot or risk becoming pregnant if she doesn’t use another form of contraception. Depo Provera has one of the highest discontinuation rates of any modern contraceptive. A woman who uses Depo has a 30 times greater chance of becoming pregnant during the first year of usage than a woman who uses a Mirena IUD. The average weight gain by women who use Depo is 5.4 lbs during the first year, and women who are already overweight tend to gain much more. It works by preventing ovulation, causing the cervical mucous to thicken to prevent sperm from entering, and makes the endometrium thinner to help prevent implantation. The advantages can include decreased period flow, less cramping, and a decreased risk of uterine and ovarian cancers. The disadvantages can include headaches and irregular period flow. The failure rate is 6% during a year of typical use.