One of the most common myths about birth control is that it can make you fat. After studying The Pill for decades on hundreds of thousands of women, the answer is NO. There is no association between taking The Pill and weight gain.
When looking at a short term 6 month time period, a significant change in weight gain was not seen in Pill users. A study from Sweden tracked more than 1,000 women over 20 years and found no association between weight gain and use of the Pill.