Effectiveness depends on returning on time: Risk of pregnancy is greatest when a woman is late for an injection or misses an injection.

• As commonly used, about 3 pregnancies per 100 women using monthly injectables over the first year. This means that 97 of every 100 women using injectables will not become pregnant.
• When women have injections on time, less than 1 pregnancy per 100 women using monthly injectables over the first year (5 per 10,000 women).

Return of fertility after injections are stopped: An average of about 5 months, one month longer than with most other methods (see Question 11).

Protection against sexually transmitted infections (STIs): None