Fifty percent of young women did not resume using condoms after they stopped taking hormonal contraception pills, according to a study conducted by Stanford Medical School researchers.

The trial followed 1,194 sexually active young women who went to Planned Parenthood clinics with the intent of beginning a contraceptive routine with hormonal pills, injections, patches or vaginal rings. None of the subjects were planning to become pregnant within a year of starting to use contraceptive measures.

At the beginning of the trial, 36 percent of the young women, ages 15 to 24, reported using condoms on a regular basis. Within three months of starting to use contraceptive pills, condom usage had gone down to 27 percent. Over the course of the trial, some of the women decided to stop taking hormonal contraception pills, 50 percent of whom did not go back to the original rate of condom usage.

Lead researcher Rachel Goldstein, a pediatric resident at Lucile Packard Children’s Hospital, said that the most influential factor in condom use is what the woman’s sexual partner thinks about condoms.

Young women in the study who reported that their partner thought condom use was “very important” or did not know what their partner thought were more likely to use condoms than subjects who thought that their partner saw condoms as “not at all important.”

The study was published in in the Journal of Adolescent Health online on Oct. 12. Research collaborators include doctors at the University of California-San Francisco.