“Depo” almost always refers to Depo-Provera, the brand name for a birth control shot given once every three months. The full name of the drug is depot medroxyprogesterone acetate, often shortened to DMPA. The word “depot” in medicine means a slow-release injection, one where the medication is deposited into muscle or fat tissue and gradually absorbed over weeks. So when someone says “I’m on depo” or “I got my depo shot,” they’re talking about this long-acting hormonal contraceptive.
How the Depo Shot Works
The injection delivers a lab-made version of progesterone, a hormone your body naturally produces during your menstrual cycle. This synthetic version stops your ovaries from releasing eggs each month. It also thickens the mucus at the opening of your cervix, making it harder for sperm to reach an egg even if one were released.
There are two versions of the shot. The original is injected into a large muscle (usually the upper arm or buttock). A newer, lower-dose version goes just under the skin and can sometimes be self-administered at home. Both follow the same schedule: one injection every 13 weeks.
How Effective It Is
With perfect use, meaning you get every shot exactly on time, the failure rate is just 0.2% in the first year. In real life, where people sometimes miss or delay appointments, about 6 out of 100 users become pregnant in the first year. That gap between perfect and typical use is almost entirely explained by late or missed injections.
If you’re late for your next shot, the CDC allows a grace period of up to two weeks (so up to 15 weeks from the last injection) without needing backup contraception. If you’re more than two weeks late, you’ll need to use condoms or abstain for seven days after receiving the shot, and you should confirm you’re not already pregnant.
Changes to Your Period
Irregular bleeding is the most common side effect in the first few months. Many users experience spotting, longer periods, or unpredictable bleeding patterns early on. Over time, though, the trend moves in the opposite direction. After one year of use, a large percentage of users stop getting their period altogether. This is not harmful. It simply means the hormone is keeping the uterine lining thin enough that there’s nothing to shed each month. Periods return after you stop the injections.
Weight and Bone Density
Weight gain is a commonly reported concern. Clinical data shows an average gain of about 5 pounds (2.4 kg) while on the shot, though individual experiences vary widely. Some users gain more, some gain nothing at all.
A more serious consideration involves bone density. The FDA requires a boxed warning on Depo-Provera stating that users may lose significant bone mineral density, and that this loss increases the longer you use the shot. The warning specifically notes that bone loss may not be completely reversible. Because of this, the recommendation is to avoid using the shot for longer than two years unless other birth control methods aren’t a good fit for you. This is especially relevant for teenagers and young adults, who are still building bone mass that will protect them later in life.
How Long Fertility Takes to Return
Unlike the pill or an IUD, the depo shot can delay your return to fertility for several months after your last injection. The median time for ovulation to resume is roughly six to seven months after the final shot. For some people it comes back sooner, around three and a half months. For others it can take close to a year. By 12 months after the last injection, about 97% of users have ovulated again. If you’re planning a pregnancy in the near future, this delay is worth factoring into your timeline.
Who Should Avoid It
The shot is not appropriate for everyone. It’s contraindicated for people with a current or past diagnosis of breast cancer, unexplained vaginal bleeding, a history of blood clots or stroke, liver disease, or known pregnancy. If you have a family history of breast cancer or a personal history of certain other cancers (endometrial or renal), this method is also generally off the table.
Other Uses of the Word “Depo”
Outside of birth control, you might occasionally see “depo” in a legal context. In law, “depo” is shorthand for “deposition,” a recorded statement given under oath before a trial. The meaning is usually clear from context: if someone mentions it in a health or pharmacy setting, they mean the shot. If it comes up in a legal conversation, it’s about testimony.