Nothing... since at least 98% of the population uses already.
/forgotten sarcasm tag.
Would that be the study that canvassed only women of child-bearing age who don't want a baby? The one that didn't break out chemical, barrier or natural means of birth control? (I don't have the link, but I saw this on FR, a Guttmacher Institute study, IIRC.)
Somewhat related: one wonders why a generation that gets insists on produce that is "organic," free-range chickens, and "all-natural" ingredients, and goes nutty over giving hormones to cows that will show up in milk happily laps up the hormones in the Pill. And haven't there been studies that show all these hormones make their way into the water with deleterious effects on fish or something? Well, maybe only one study by people who never got funding again . . .