- sexually active women of child-bearing potential not actively practicing birth control by using a medically accepted device or therapy (that is, intrauterine device, hormonal contraceptive, or barrier devices) during the study period (at least 24 months); since doxycycline may interfere with the effectiveness of hormonal contraceptives, sexually active women of child-bearing potential who use a hormonal contraceptive will be required to use a second form of contraception to safeguard against contraceptive failure while participating in the study