[areafiftyone]

It does stop pregnancy if it doesn't break. of course the only thing stops it 99.9% of the time besides abstinance is the pill.

[jaydubya2]

It does stop pregnancy if it doesn't break. of course the only thing stops it 99.9% of the time besides abstinance is the pill.
Or the Natural Family Planning method, if used correctly.

[the OlLine Rebel]

Abstinence stops EVERYTHING 100% of the time.

[Protagoras]

Abstinence is 100%.

The pill is the following:

Efficiency
With perfect use, the birth control pill can be as much as 99% effective.
However, perfect use means remembering to take the Pill everyday at the same time and to be in good health, under the age of 35 and a nonsmoker.
With typical use, the average failure rate is between 3 and 13% per year, depending on the type of pill you are taking.
Certain factors can decrease the efficiency of the contraceptive pill, though. These factors include:
Taking antibiotics
Taking certain medications, include oral vaginal infection medication, certain anti-seizure drugs and certain HIV drugs
Having diarrhea or vomiting
Taking St. John's Wort
Taking Orlistat (not confirmed)
The birth control pill is not recommended for women who smoke, have certain health conditions or are over the age of 35.

(bold mine)