Medroxyprogesterone is a synthetic form of progesterone, and yes, it is used as birth control. You may know it better by the brand name Depo-Provera, the injectable contraceptive given once every three months. That said, medroxyprogesterone also comes in oral tablet form for non-contraceptive purposes, which is where the confusion often starts. The pill version treats irregular periods, abnormal uterine bleeding, and other hormonal conditions but is not prescribed as a contraceptive. When people refer to medroxyprogesterone as birth control, they’re talking about the injection.
How It Prevents Pregnancy
The injectable form works through three overlapping mechanisms, which is part of why it’s so effective. First, it signals the brain to stop triggering ovulation. Specifically, it reduces the hormonal surge that causes an egg to mature and release each month. No egg means no fertilization.
Second, it thickens cervical mucus, making it much harder for sperm to travel into the uterus. Third, it changes the uterine lining so that even in the unlikely event an egg were fertilized, implantation would be difficult. These three layers of protection working together give the shot a very low failure rate when used correctly.
How Effective Is the Shot?
With perfect use, meaning you get every injection exactly on schedule, the failure rate is just 0.2% in the first year. Under typical use, which accounts for people who sometimes show up late for their appointment, the failure rate rises to about 6%. That gap is almost entirely explained by missed or delayed injections, so staying on schedule is the single most important thing you can do to keep the shot working.
What the Injection Schedule Looks Like
Depo-Provera comes in two formulations. The original intramuscular version delivers 150 mg and is injected into the upper arm or buttock by a healthcare provider. The newer subcutaneous version delivers 104 mg and is injected into the thigh or abdomen, sometimes by the patient themselves.
Both versions follow the same timing: one injection every 12 to 14 weeks. If more than 14 weeks pass between shots, you’ll need a pregnancy test before receiving the next one. Many clinics will set a recurring appointment to help you stay in that window.
Common Side Effects
The most noticeable side effect for most people is a change in menstrual bleeding. Irregular spotting is common in the first few months. Over time, periods often become lighter, and many users stop having periods altogether after the first year. This is not harmful; it simply reflects the thinned uterine lining and suppressed ovulation.
Weight gain is another frequently reported side effect. Studies vary, but many users gain a modest amount over the first year, with the effect potentially increasing the longer you stay on the shot. Other possible side effects include headaches, mood changes, decreased sex drive, and breast tenderness. These tend to be most noticeable in the first few months as your body adjusts.
Because the injection lasts three months, side effects can’t be “turned off” the way you could stop taking a daily pill. If you experience something unpleasant, you’ll generally need to wait for the dose to wear off gradually.
The Bone Density Warning
The FDA places its most serious type of warning on Depo-Provera regarding bone mineral density. Users may lose significant bone density, and the loss increases with longer use. Some of that bone loss may not fully reverse after stopping. Because of this, the FDA recommends that Depo-Provera not be used as a long-term method for longer than two years unless other birth control options are considered inadequate.
This is especially relevant for teenagers and young adults, who are still building peak bone mass. It’s unknown whether using the shot during this critical window permanently reduces lifetime bone strength or increases fracture risk later in life. If you’re considering the shot for more than two years, this tradeoff is worth a direct conversation with your provider.
How Long Fertility Takes to Return
One of the biggest practical considerations with Depo-Provera is that fertility doesn’t bounce back immediately. On average, ovulation returns about 7 months after the last injection. Some people ovulate as early as 3.5 months after their final shot, while others take nearly 12 months. By the end of one year after the last injection, about 97% of users have ovulated at least once.
This delay is important if you’re planning a pregnancy in the near future. Unlike the pill or an IUD, where fertility typically returns within weeks, the shot requires more lead time. If you think you might want to conceive within the next year, a shorter-acting method may be a better fit.
Pill vs. Shot: Same Drug, Different Purpose
The oral tablet form of medroxyprogesterone (brand name Provera) uses much lower doses and is prescribed for conditions like irregular periods, endometriosis-related pain, and abnormal uterine bleeding. It is not effective as birth control at those doses. The contraceptive effect depends on the sustained, high-dose delivery that only the injection provides. So if you’ve been prescribed medroxyprogesterone tablets, those are not protecting you from pregnancy, and you’d need a separate contraceptive method.