How long does it take for breasts to swell when on birth control pills?

Within a few days: Your breasts will respond to the estrogen-like component of your birth control pills within 24 hours to a few days. You may experience tenderness, swelling, or even some clear nipple discharge -- all of this is normal.

Maybe never: Sometimes they don't swell as the dose of hormones may be too low to affect them- or they could in a couple of days.

May not happen: Not everyone gets breast swelling with birth control use. This can be a side effect of birth control pills but not all side effects are experienced by individuals who take the medication.