The birth control implant, known most commonly as Nexplanon, is a thin, flexible rod inserted under the skin of the upper arm. As a long-acting reversible contraceptive (LARC), it works continuously for up to three years. For many considering its use, weight gain remains the most frequently discussed potential side effect. This concern often stems from historical associations between older, higher-dose hormonal contraceptives and body weight changes. Understanding the true relationship between the implant and weight requires examining the specific hormone it uses and the scientific data.
Clinical Evidence on Weight Change
Clinical studies and systematic reviews show that for the majority of users, the etonogestrel implant does not cause statistically significant weight gain compared to individuals not using hormonal birth control. The average weight change observed in implant users over the three-year use period is minimal. Some studies report an average gain of less than five pounds, which is comparable to the natural weight fluctuation seen in the general population of reproductive-aged women.
One study comparing implant users to those using a non-hormonal copper IUD found that implant users gained an average of 6.6 pounds over three years, while IUD users also gained 2.4 pounds. This highlights that some weight change occurs regardless of the contraceptive method chosen. A significant portion of women using the implant experience no weight change or even a slight weight loss. The perception of widespread weight gain is often greater than the reality demonstrated by objective clinical measurements.
How the Hormone Affects Metabolism
The birth control implant releases a steady, low dose of the synthetic progestin called etonogestrel. This hormone acts by suppressing ovulation, thickening cervical mucus, and thinning the uterine lining. Etonogestrel differs structurally and functionally from natural progesterone, which can influence metabolic processes in susceptible individuals.
Progestins may temporarily affect appetite regulation, possibly leading to a slight increase in caloric intake for some users. Some hormonal contraceptives can also cause temporary water retention. This fluid retention is not true fat gain, but it can lead to feelings of bloating and a small, temporary increase on the scale.
The specific mechanism that causes weight changes in the small subset of women who do experience significant gain is not fully understood, but emerging research points toward genetic factors. Studies have identified certain genetic variants that may predispose some individuals to greater weight gain while using the implant. Higher baseline body mass index (BMI) has also been associated with a greater likelihood of weight gain for some users. The low-dose, continuous release of etonogestrel does not appear to trigger a major metabolic shift resulting in substantial fat accumulation for the vast majority.
Identifying Non-Implant Related Weight Gain
The life stage during which women typically use the implant is naturally prone to weight gain. For the average woman, gaining about one to two pounds per year is common due to non-contraceptive factors alone. This gradual increase is often attributed to a natural slowdown in metabolism that occurs with age and lifestyle changes.
Factors such as transitioning out of high school or college, changes in diet, reduced physical activity, or increased stress levels can all contribute to weight gain mistakenly attributed to the implant. Stress triggers the release of cortisol, which can increase appetite and promote fat storage. Furthermore, women who switch from a combined hormonal contraceptive might perceive subsequent weight change as implant-related if the previous method masked fluid retention or appetite changes.
Next Steps and Alternative Options
If you are using the etonogestrel implant and are experiencing unwanted or rapid weight gain, consult with a healthcare provider. A doctor can help determine if the weight change is truly related to the implant, or if it is due to other underlying causes such as thyroid issues or lifestyle changes. It is inadvisable to remove the implant solely based on weight concerns without a medical discussion, as this can disrupt effective contraception.
For those who decide the implant is not the right fit, several effective alternatives may address weight concerns. Non-hormonal methods, such as the copper intrauterine device (IUD), eliminate hormonal side effects. Barrier methods, like condoms or diaphragms, also contain no hormones. Other progestin-only options, such as some hormonal IUDs, deliver the hormone locally to the uterus, resulting in lower systemic exposure than the implant and potentially minimizing side effects.