It's rare, but some women do gain a little bit of weight when they start taking birth control pills. It's often a temporary side effect that's due to fluid retention, not extra fat. A review of 44 studies showed no evidence that birth control pills caused weight gain in most women.

Which contraceptives cause weight gain?

There are 2 methods of birth control that cause weight gain in some people who use them: the birth control shot and the birth control implant. But this doesn't happen to everybody who uses these types of birth control. Many people use the shot or the implant without gaining weight.

Does birth control affect weight loss?

Yes, but it is important to understand that despite what the evidence suggests, everybody is different and may react differently to hormones in birth control pills. Many studies found that some participants lost weight whereas others gained a few pounds while on the pill.