There are no "absolutes" when dealing with birth control pills. Much of how people react to medications depends on how much of the drug is metabolized, where it is metabolized, the contents of the stomach, the time of day it is taken, etc.

Some women lose weight on birth control pills, some gain and, of course, some stay the same.

Robert Hatcher, in his text, "Contraceptive Technology," states: "In most instances, weight change is minimal and is unrelated to pill use. Approximately as many women lose weight as gain weight while taking oral contraceptives. In some women, however, weight gain is definitely caused by oral contraceptives. Rarely, pills can cause a gain of 10 to 20 pounds or more."

When it is related to the pill, weight gain can be due one or more causes:

Fluid retention due to the estrogen or progestin component of the pill. This pattern of weight gain occurs in the month or so after initiating pills.

Estrogen-induced weight gain increases subcutaneous fat, particularly in the hips, thighs and breasts, typically occurring after several months on pills.

Increased appetite and increased intake of food occurring over several years.

Depression accompanied by an increased intake of calories and/or a decrease in exercise. If weight gain is a problem, Hatcher recommends switching to a pill with less androgenic potency (stay away from levonorgestrel containing pills).

You can try to decrease the estrogen, progestin or both. You also can try to increase the estrogen potency, if the weight gain is due to increased breast tissue and subcutaneous fat, particularly in thighs and hips.