The Depo-Provera shot is FDA-approved and considered safe for most women, but it carries specific risks that set it apart from other birth control options. The most significant: it can cause bone density loss that increases with longer use and may not fully reverse after stopping. The FDA has placed its strongest warning label on the shot for this reason, recommending it not be used for longer than two years unless other methods aren’t a good fit.
That doesn’t mean the shot is dangerous for everyone. Millions of women use it without serious problems. But understanding what the real risks are, how common side effects actually happen, and who should avoid it entirely will help you decide whether it’s the right choice for your body.
How the Depo Shot Works
Depo-Provera is an injection of medroxyprogesterone acetate, a synthetic version of the hormone progesterone. You get the shot once every three months, typically in your arm or buttock. It prevents pregnancy in three ways: it stops your ovaries from releasing eggs, thickens the mucus at your cervix so sperm can’t get through, and thins the lining of your uterus.
With perfect use (getting your shot exactly on time every 12 weeks), the failure rate is just 0.2%. In typical real-world use, where people sometimes miss or delay appointments, the failure rate is about 6%. That gap is worth noting. The shot works extremely well when you stay on schedule, but a late injection leaves you more exposed than you might expect.
The Bone Density Warning
The FDA’s black box warning, issued in 2004, is the most serious safety concern attached to the shot. Women who use Depo-Provera lose bone mineral density over time. The longer you use it, the more bone you lose, and some of that loss may be permanent.
This is especially important for teenagers and women in their early twenties. Your body is still building bone mass during those years, reaching a lifetime peak sometime in your mid-to-late twenties. It’s unknown whether using the shot during this critical window reduces the peak bone mass you ultimately achieve, which could raise your risk for osteoporosis and fractures decades later. The FDA’s recommendation is clear: Depo-Provera should not be used as a long-term method (more than two years) unless other contraceptive options are inadequate for you.
ACOG, the main professional organization for OB-GYNs, has acknowledged this concern while also noting that for many women, the benefits of reliable contraception outweigh the bone density risk. If you’ve been on the shot for a while and are thinking about continuing, it’s a conversation worth having with your provider about your individual risk factors, including your family history of osteoporosis and whether you get enough calcium and vitamin D.
Common Side Effects and How Often They Happen
In a large clinical trial following over 3,900 women for up to seven years, the side effects reported by more than 5% of users were menstrual irregularities (including both irregular bleeding and no periods at all), abdominal discomfort, dizziness, weight changes, nervousness, headache, and fatigue.
Irregular bleeding is the most common reason women are caught off guard. In the first few months, spotting or unpredictable bleeding is typical. But this shifts over time. By 12 months, 57% of women on the shot had stopped getting periods entirely. By 24 months, that number climbed to 68%. For some women, losing their period is a welcome side effect. For others, the months of irregular bleeding before that point are a dealbreaker.
Weight gain is real and tends to be gradual. In clinical data, women gained an average of about 2.5 kg (roughly 5.5 pounds) after one year, 3.7 kg (about 8 pounds) after two years, and 6.3 kg (nearly 14 pounds) after four years. Some women gain significantly more, and about 2% of participants in the large trial dropped out specifically because of weight gain. This isn’t a side effect that affects everyone equally, but it’s consistent enough to plan for.
Less common side effects, reported by 1% to 5% of users, include decreased sex drive, depression, back pain, leg cramps, breast pain, acne, hair thinning, insomnia, nausea, bloating, and hot flashes.
Breast Cancer Risk
The available evidence from epidemiological studies suggests that current use of Depo-Provera is associated with roughly a 1.5 to 1.65-fold increase in breast cancer risk. To put that in perspective, if your baseline risk of being diagnosed with breast cancer in a given period is low (as it is for most younger women), a 50-65% relative increase still translates to a small absolute increase. But if you have a family history of breast cancer or other factors that already elevate your risk, this is something to weigh carefully.
This increased risk appears linked to current use. The data doesn’t suggest the same elevation persists long after stopping the shot, though research on long-term outcomes is still limited.
Who Should Not Use It
Depo-Provera is not appropriate for women with a history of breast cancer, since the hormone can stimulate breast tissue. It’s also not recommended for women with active liver disease, unexplained vaginal bleeding that hasn’t been evaluated, or known or suspected pregnancy. If you already have significant risk factors for osteoporosis, such as a family history, long-term steroid use, or an eating disorder, the bone density effects make the shot a poor fit.
One advantage the shot does have over combined hormonal methods (those containing estrogen): it doesn’t carry the same elevated risk of blood clots. That makes it a safer option for women who can’t use estrogen-based contraceptives because of migraine with aura, a history of deep vein thrombosis, or other clotting concerns.
What Happens When You Stop
Unlike the pill or an IUD, the effects of the Depo shot don’t wear off quickly. After your last injection, it takes time for the hormone to clear your system and for your natural cycle to return. The median time to pregnancy after stopping is about 9 months from the last injection, but the range is wide: some women conceive within 4 months, while others wait 18 to 24 months or longer.
If you’re planning to get pregnant within the next year or two, this delayed return to fertility is worth factoring into your decision. Switching to a shorter-acting method ahead of time gives your body more flexibility on timing.
Putting the Risks in Context
Every contraceptive method carries tradeoffs. The Depo shot is highly effective, requires no daily effort, and is a good option for women who can’t use estrogen. Its biggest downsides are the bone density loss with extended use, gradual weight gain, and the long timeline for fertility to return after stopping. The breast cancer signal deserves attention but represents a modest absolute risk increase for most users.
For short-term use (under two years), the safety profile is straightforward for most healthy women. Beyond two years, the calculus shifts, and you’ll want to actively evaluate whether the convenience of the shot justifies the cumulative bone density loss compared to alternatives like a hormonal IUD, implant, or progestin-only pill that don’t carry the same bone concerns.