The question of whether hormonal birth control causes weight gain is one of the most common inquiries people have when considering contraception. Many individuals express concern that weight gain might be an unavoidable side effect, which often leads them to discontinue a beneficial method. To address this, it is important to understand the specific type of contraception in question: progesterone-only methods, which use synthetic forms of the hormone progesterone known as progestins.
Understanding Progestin-Only Contraception
Progestin-only contraception utilizes synthetic progesterone (progestin) to prevent pregnancy by thickening cervical mucus and, in some cases, suppressing ovulation. These methods are distinct from combined hormonal contraceptives, which contain both a progestin and an estrogen component. Progestin-only options are often chosen by individuals who cannot use estrogen due to medical conditions or personal preference.
The available forms of progestin-only contraception include:
- The Progestin-Only Pill (POP), sometimes called the mini-pill.
- The hormonal implant placed under the skin.
- The hormonal Intrauterine Device (IUD).
- The injectable contraceptive.
What Clinical Studies Show About Weight Gain
For the majority of progestin-only methods, clinical research shows that the average weight change experienced by users is minimal and often comparable to that of non-users. Meta-analyses and large studies examining progestin-only pills, hormonal implants, and hormonal IUDs generally report a mean weight gain of less than 2 kilograms (4.4 pounds) over the first 12 months. This small change is often not considered statistically significant when compared to control groups.
The notable exception among progestin-only methods is the depot medroxyprogesterone acetate (DMPA) injection, commonly known as the birth control shot. Some studies have shown that DMPA users experience a small but measurable average weight gain, with reports suggesting an average gain of around 5 pounds after one year of use. Longitudinal studies following users for multiple years have reported a more substantial average increase, sometimes up to 11 pounds over three years.
It is important to understand that this average figure is not universal, as approximately 75% of DMPA users experience little to no significant weight change. However, a specific subset of users, sometimes referred to as “early gainers,” are at higher risk for more substantial weight gain. These individuals, defined as those who gain more than 5% of their initial body weight within the first six months, may continue to gain significant weight, averaging as much as 24 pounds over three years of use.
Furthermore, research has indicated that some progestin-only methods may cause changes in body composition even when overall weight gain is small. Studies have shown users of hormonal IUDs and progestin-only pills can experience an increase in body fat percentage and a corresponding decrease in lean body mass compared to those using non-hormonal methods.
How Progestins May Affect Body Weight
The biological mechanisms by which progestins could influence weight are complex and are thought to involve several internal processes. One leading hypothesis is that synthetic progestins may affect appetite regulation, potentially increasing feelings of hunger. This is supported by the natural effects of progesterone, which is known to have an orexigenic, or appetite-stimulating, effect during the luteal phase of the menstrual cycle.
This appetite increase may be linked to the interaction of progestins with gut hormones that signal hunger and satiety, such as ghrelin and leptin. An alteration in the balance of these hormones could lead to increased caloric intake, which, over time, results in true fat accumulation. The changes in body composition noted in some studies, such as increased body fat and decreased lean mass, suggest a shift in metabolism or fat storage.
Another factor that can contribute to a temporary increase on the scale is fluid retention, often described as bloating. Progestins can sometimes cause the body to hold onto more water, leading to a temporary weight increase that is not true fat gain. This fluid retention is a common side effect of many hormonal changes.
Other Reasons for Weight Change While Using Birth Control
It is often challenging to isolate the effect of contraception from the many other factors that contribute to weight change in young adults. The years during which many people begin using hormonal birth control—late adolescence and early adulthood—are already a time when weight gain is common due to natural life transitions. Factors such as the metabolic slowdown that occurs with increasing age can make weight gain an expected occurrence for anyone, regardless of contraceptive use.
Significant lifestyle changes, such as starting college, altering diet and exercise habits, or experiencing higher levels of stress, are major determinants of weight gain in this age group. For example, stress can cause the body to release cortisol, a hormone that promotes fat storage, while lack of sleep can disrupt the balance of appetite-regulating hormones.
These external, non-contraceptive factors mean that weight gain attributed to birth control is often a result of correlation rather than direct causation. The weight changes experienced by users may simply be the normal weight trajectory of their age group, coinciding with the start of a new medication. By considering these confounding variables, users can better understand the true impact of their contraceptive method.