Females of the child bearing age release eggs (ova) from the ovaries (female sex organ), usually every 28 days. A pregnancy results when an egg combines with a sperm (fertilization). The main action of implants is to prevent this release of eggs (ova).
In addition it thickens the cervical mucus making the sperm migration difficult, within the female reproductive tract.
Also, it makes the uterine lining (lining of the womb) thin so that the implantation of the embryo (early pregnancy stage) will not take place.
Changes in your period – You won’t have your period every month, but instead have irregular, unpredictable bleeding. This is annoying but not a serious problem. Many women stop having their menstrual periods while on depo provera which is not a reason to worry. You will get your menstrual periods back within 6 to 18 months after you stop taking the injection.
Weight gain – due to increased appetite. This can be controlled by regular exercise and taking a healthy diet.