I seem to remember most studies showing that weight gain due to the Pill is usually about 5 lb of water weight on average. Everything else can usually be attributed to the time of life when people usually start the Pill (tail end of puberty when there's natural weight gain, or away from home for the first time, or starting a new relationship, etc.) Individual experience may vary.
One way or another, I know that the medications I'm on now contributed to my weight gain, and I've still lost. I know that others here have lost weight even while on meds that cause severe weight gain. So, don't let the rumours discourage you!
