How effective is the birth control pill called tri sprintec when on accutane

Very effective, but: The oral contraceptive pill is very effective, but, it must be taken everyday at the same time each day. The failure rate is less than 2 per thousand. Many patients on Accutane also use a "backup" method such as a vaginal or condom contraceptive in conjunction with the pill to eliminate even that small risk to prevent unintended pregnancy with birth defects with the medication.