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Both patients and doctors often think that the use of hormonal birth control can lead to weight gain. Sometimes, this belief can make women feel hesitant about using hormonal birth control, especially when they already suffer from overweight or obesity. Is it scientifically proven that hormonal birth control causes weight gain, though? Let's find out.
Estrogen and Progestin, the Villains of the Story
Estrogen and progesterone are both female hormones that play a very important role in the menstrual cycle and the preparation of the uterus for a possible fertilization. The levels of these two hormones are at their lowest just before menstruation. Then, they start to rise again when the follicle that contains the egg starts to develop. After an ovary releases an egg, both estrogen and progesterone cause the thickening of the lining of the uterus in case the egg is fertilized and needs a proper surface to attach too. 
Synthetic estrogen and progesterone, known as progestin, are manufactured to treat health problems related to hormonal imbalances in women, for example, during menopause. Women going through menopause usually take estrogen to compensate the lack of natural hormones during this phase. 
Types of Hormonal Birth Control
Nowadays, there are several types of hormonal contraceptives, which not only vary in their form of administration but also in their composition. All of them contain the synthetic versions of estrogen and progesterone, which are normally present in a woman's body. 
Birth control pills are one type of hormonal contraceptive. They are made of a combination of estrogen and progestin. There is also the mini pill, which only contains progestin, since some women are not able to take progestin or just want to avoid the side effects that this substance causes. The pill does not stop your menstruation, unless you take two treatments without leaving a week in between them and you have to take it every day, at the same time, for 28 days in a row.
See Also: Side Effects of Birth Control Pills
Most of them stop menstrual cycles and release the hormonal load gradually, as if you were taking the pill every day. Their advantage is that you don't have to worry about remembering to take them every day, as they can be effective for months or even years at a time.
All of these birth control methods have a certain amount of hormones that thicken the mucus of the vagina and avoid the release of the egg by the ovary in order to prevent pregnancy.