How effective is seasonale?

Very: All birth control pills are very effective with less than 1% failure rate if used properly. Seasonale is designed to reduce menstrual periods to four episodes per year. There is, however, a 20% chance of irregular bleeding and spotting for the first few months which may not resolve in some women. If spotting occurs, birth control may not be as effective.

If taken correctly: Its as effective as any other birth control pill.