Women who take oral contraceptives can enjoy some rather pleasant side effects, including lighter periods, spot-free skin, fewer menstrual cramps and reduced risk of cervical and endometrial cancer. Some of the less favorable consequences? Increased risk of blood clots, mood swings and the dreaded weight gain. Or at least when it comes to packing on a few pounds, that’s what many have thought.

A new study from Oregon Health and Science University found that women can no longer blame those extra pounds on the Pill. Oral contraceptives in fact do not cause weight gain, which is one of the main reasons women say they stop using it as a birth control method.

Researchers compared two groups of rhesus monkeys, which have a reproductive system nearly identical to those of humans. One group of monkeys was obese, while the other group was of normal weight. When both groups took birth control pills and ate the same diet over a period of eight months, the overweight group actually lost 8.5 percent of their weight and twelve percent body fat. The normal group experienced no changes in body mass.

So what’s the culprit when women gain weight while on the Pill? Researchers say it isn’t the Pill itself. High levels of estrogen in some brands can cause excess water retention and increased appetite, but experts say these symptoms usually taper off as the body acclimates to the hormones. Women who see their waistline expanding could just be experiencing normal weight gain associated with aging. Or they might actually be eating more than they realize.

Oral contraceptives remain one of the most effective forms of birth control, with a 99.9 percent rate of preventing pregnancy when taken correctly — so many women agree they’re worth sticking with if you don’t want a baby yet. Until then, eat for one, rather than two.