**2.4 Effectiveness**

The efficacy, or failure, of COCs can differ considerably based on the type of user. The perfect user never misses taking a pill, takes the pill at the same time each day, and never vomits or has diarrhea. The failure rate for perfect users is <1 pregnancy per 100 women (or 3 per 1000 women). In turn, the typical user's behavior results in the failure rates reported for the general population, which is 5–8 pregnancies per 100 women in the first year [34–38].

It is important to note that the risk of pregnancy is greatest when a woman starts a new pack of pills 3 or more days late or misses 3 or more pills near the beginning or end of a pack.
