How effective is the birth control pill if you're highly fertile?

Very: If you take birth control pills and don't accidentally skip any pills, they are 99% effective. Occasionally other medicines you may take can interfere with the birth control pills so you should let your doctor know about any other medicines you are taking.

Excellent, but...: With no missed pills, "perfect use", the failure rate is 0.3%->99% effective.In typical use, because taking a pill every d without ever missing is hard, about 9/100 couples will get pregnant/year.Effective after 7 days.If you have a hard time remembering daily meds, ask your doctor about long-acting reversible contraception(larc)--iuds or an implant under the skin-easy, very effective, lasts 3-10 yrs.