How long does a progestin injection last? Unpacking the timeline and effects

October 9, 2025 •

4 min read

The progestin injection, most commonly known by the brand name Depo-Provera, provides contraceptive protection for approximately 12 to 14 weeks, requiring a repeat injection every three months for continued effectiveness. This popular, long-acting birth control method utilizes a synthetic hormone to prevent pregnancy.

Quick Summary

Progestin injections, like Depo-Provera, last for 12 to 14 weeks by preventing ovulation. A shot is required every 12 weeks for sustained effectiveness. Fertility returns after discontinuation but may be delayed.

Key Points

Standard Duration: A single progestin injection, like Depo-Provera, lasts for 12 to 14 weeks, requiring a repeat shot every 3 months for continuous protection.
High Effectiveness: When used perfectly and on schedule, the shot is over 99% effective at preventing pregnancy.
Mechanism of Action: It works by preventing ovulation, thickening cervical mucus, and thinning the uterine lining.
Delayed Return to Fertility: On average, it can take 10 months to over a year for fertility to return after the last injection, which is an important consideration for family planning.
Bone Density Concerns: Long-term use (more than two years) has been associated with a decrease in bone mineral density, leading to an FDA warning.
Estrogen-Free Option: The progestin-only formulation makes it a suitable contraceptive choice for women who cannot use estrogen.

The duration of a progestin injection is a crucial factor for anyone considering this method of birth control. The most widely used type, Depo-Provera, is well-known for its three-month effectiveness, offering a convenient, highly reliable option for pregnancy prevention. A clear understanding of its timeline, mechanism, and associated effects is essential for making an informed decision about reproductive health.

The 3-Month Contraceptive Cycle

A standard progestin injection, containing medroxyprogesterone acetate (MPA), provides contraceptive protection for approximately 12 to 14 weeks. The injection is administered into a muscle (intramuscularly, like Depo-Provera) or just under the skin (subcutaneously, like Depo-subQ Provera 104). For continued protection, a repeat injection must be received on a strict schedule, typically every 12 weeks. Adherence to this schedule is critical for maintaining its high efficacy.

Perfect Use vs. Typical Use: With perfect use—meaning every shot is received on time, every 12 weeks—the injection is over 99% effective at preventing pregnancy. In real-world, or typical use, its effectiveness is about 96%, as some individuals may miss or delay their scheduled injection.
The Grace Period: Healthcare providers often allow for a small grace period for late injections, typically up to 2 weeks (totaling 14 weeks from the last injection). However, if an injection is delayed beyond 15 weeks, a pregnancy test may be necessary before the next dose, and a backup contraception method is recommended for the following week.

How the Progestin Injection Works

Progestin injections contain a synthetic version of the hormone progesterone. The MPA in the injection prevents pregnancy through a few primary actions:

Inhibits Ovulation: It prevents the ovaries from releasing an egg, so no egg is available for fertilization.
Thickens Cervical Mucus: The progestin causes cervical mucus to become thicker and stickier, creating a barrier that is difficult for sperm to pass through.
Thins the Uterine Lining: It thins the endometrium, making it less receptive to a fertilized egg.

What Happens When You Stop the Progestin Injection

One of the most significant differences between progestin injections and other birth control methods is the time it takes for fertility to return after discontinuation. Because the hormone is gradually released over time, it takes a while for its effects to fully wear off. On average, it takes about 10 months to a year for fertility to return, but it can be longer for some women. The duration of use does not affect the time it takes to become pregnant after stopping the injections. This prolonged delay is an important consideration for individuals who plan to start a family in the near future.

Benefits and Risks of Progestin Injections


Feature	Benefits	Potential Risks
Effectiveness	Highly effective, with over 99% efficacy with perfect use.	High efficacy relies on consistent, on-schedule injections.
Convenience	Requires a shot only once every 3 months; no daily pill to remember.	Can feel inconvenient to visit a provider for a shot every 12 weeks.
Hormonal Composition	Estrogen-free, suitable for women who cannot use estrogen-containing methods.	Potential for hormonal side effects like mood changes, headaches, and weight gain.
Menstrual Cycle	Can lead to lighter periods or amenorrhea (absence of periods), which some find beneficial.	Can cause irregular bleeding or spotting, particularly during the first year of use.
Long-Term Use	Protects against endometrial cancer.	May cause bone density loss, particularly with prolonged use (more than 2 years), leading to a black box warning from the FDA.

Making an Informed Choice

When considering a progestin injection, a thorough discussion with a healthcare provider is essential. They can assess individual health history and risk factors, such as bone density concerns or pre-existing conditions like depression. Individuals with risk factors for bone loss may be advised to limit use to two years and ensure adequate calcium and vitamin D intake.

Additionally, patients should be aware of the range of side effects and how to manage them. Resources like the Centers for Disease Control and Prevention (CDC) offer valuable guidance on injectables and management of side effects. Other options, including long-acting reversible contraceptives (LARCs) like IUDs and implants, may offer higher effectiveness without the need for regular appointments.

Conclusion

A progestin injection typically provides contraception for 3 months, offering a convenient, highly effective method of birth control for many women. Its main function is to prevent ovulation, with a reliance on regular, scheduled injections to maintain efficacy. While it provides numerous benefits, such as not containing estrogen and potentially reducing menstrual bleeding, it's also associated with potential risks, including a delayed return to fertility and bone density loss with long-term use. Understanding these aspects allows individuals to weigh the pros and cons against their personal health needs and reproductive goals.

Frequently Asked Questions

A Depo-Provera injection provides contraceptive protection for 12 to 14 weeks, which is why a repeat shot is needed every three months (12 weeks).

If you are more than 15 weeks late for your injection, you may need a pregnancy test before receiving the next shot. You should also use a backup birth control method for the following seven days.

Fertility may be delayed after stopping the shot. On average, it can take about 10 months to over a year for regular ovulation to resume, though some women may conceive sooner or later.

No, the progestin injection does not cause permanent infertility. The delay in returning to fertility is temporary, and most women can and do become pregnant after stopping the shots.

Yes, there are different types. The most common in the US are Depo-Provera (intramuscular) and Depo-subQ Provera 104 (subcutaneous), both lasting 3 months. Another type is norethisterone enanthate (NET-EN), which lasts for 2 months and is available in some countries.

Common side effects include irregular bleeding or spotting, weight gain, headaches, and mood changes. After about a year of use, many people experience a cessation of their periods.

The FDA recommends limiting use to two years due to potential bone density loss, unless other contraceptive methods are inadequate. However, some health organizations note that the bone loss is reversible and the benefits often outweigh the risks.