There has been nearly 40 years of experience in its use worldwide, in 15 million women, in over 90 countries. The normal dose is 150mgs every 12 weeks.
Failure rates are higher in younger more fertile women.
DMPA levels in the blood decline with time and become too low to prevent ovulation after 12 weeks. This is more rapid in very underweight women. Routinely DMPA should be started before day 5 of the cycle. Day 1 of the menstrual cycle is the first day of bleeding in a normal period. The contraceptive effect is immediate, although women are generally advised to wait 7 days before relying on the injection alone.