When Should I Take Emergency Contraceptive Pill After Unprotected Intercourse?

How effective is emergency contraception after the condom slipped? I recently had sex and the condom slipped without me and my partner realizing it. He ejaculated twice, however we used spermicide jel as a precaution. A day after the incident, I took Next Choice. How effective will that be? And also, since I have an abnormal menses cycle, will that affect how well the medication worked (spermicide/Next Choice)?