Dr. Rachel L. Goldstein, Ushma D. Upadhyay and Dr. Tina R. Raine of the Stanford Medical School said the study involved women ages 15-24 who began using oral contraceptive pills, patch, ring, or depot medroxyprogesterone and attending public family planning clinics.
The study participants completed questionnaires at the beginning of the study and at three, six and 12 months.
The researchers used multivariable logistic regression to assess baseline factors associated with dual method use at 12 months among 1,194 women who were sexually active in the past 30 days.
At baseline, 36 percent of the women used condoms and 5 percent were dual method users -- condom and a hormonal contraceptive.
Oral contraceptives provide no protection against sexually transmitted diseases, Goldstein said.
The study, published in the Journal of Adolescent Health, found after the women began using the hormonal method, condom use decreased to 27 percent and remained relatively unchanged during the study.
Women who were condom users at baseline had nearly twice the odds of being a dual method user at 12 months compared with non-users.
The women said condom use depended on their partner's views. If he thought condoms were very important then the odds of dual contraception increased.
The study was published in the Journal of Adolescent Health.