Depo-Provera (the birth control shot) is very effective at preventing pregnancy when taken on schedule, with about 99% effectiveness with perfect use and around 94% effectiveness in typical real‑life use. That means that with typical use, about 6 out of 100 people may become pregnant over a year, mostly when injections are late or missed.

Key effectiveness numbers

  • Perfect use: failure rate about 0.2% in the first year (more than 99% effective).
  • Typical use: about 6% get pregnant in a year (around 94% effective overall).
  • Protection duration: each shot protects against pregnancy for about 12–13 weeks and must be repeated roughly every 3 months.

How it works

  • Depo-Provera contains medroxyprogesterone acetate, a progestin hormone.
  • It mainly works by suppressing ovulation (stopping the ovary from releasing an egg), thickening cervical mucus, and thinning the uterine lining.
  • When injections are on time every 12–13 weeks, ovulation stays suppressed continuously, which keeps protection very high.

What affects how well it works

  • Timeliness of shots: late or missed injections are the biggest reason effectiveness drops from 99% to about 94% in typical use.
  • Access and follow‑through: needing a clinic visit or correct self‑injection every 3 months can make adherence harder for some people.
  • Certain medications that affect hormone metabolism might theoretically reduce effectiveness, so users should review other meds with a clinician.

Pros related to effectiveness

  • No daily pill to remember; only 4 injections per year when on schedule.
  • Effectiveness comparable to, or better than, many other hormonal methods and similar to modern copper IUDs when used correctly.
  • Suitable for people who cannot use estrogen‑containing methods and want long‑acting but not permanent contraception.

Important caveats

  • Does not protect against sexually transmitted infections, so condoms are still recommended for STI protection.
  • Fertility can take several months or longer to return after stopping; this is temporary but important if planning pregnancy soon.
  • There are potential side effects (irregular bleeding, weight changes, and concerns about bone mineral density with long‑term use), so benefits and risks should be reviewed with a health professional.

Information gathered from public forums or data available on the internet and portrayed here.