Birth control implants release a synthetic form of the hormone progesterone called progestin. This hormone prevents ovulation or the release of an egg. It also thickens the mucus of the cervix, making it hard for the sperm to reach an egg if the body does ovulate.
The hormone progesterone increases during pregnancy, so the implant works by making the body think it is already pregnant and has no need to release another egg.
Research is mixed on whether the implant causes weight gain or if the weight gain is due to other factors.
- Women have long complained of weight gain when using hormonal birth control.
- A 2014 Cochrane Review found no significant effects on weight.
- Changes in hormones can affect many processes within the body.
- Women should report any side effects they experience to their doctor promptly.
Theories on the implant and weight gain
There are a few theories about weight gain being caused by the birth control implant.
The research on weight gain related to birth control is mixed. If birth control implants do cause weight gain, it is not clear why this might happen.
One theory is that the hormone progestin may increase body fat. A 2015 study found a 2 percent increase in body fat among women who used the implant for 12 months.
Another possibility is that progestin causes water retention, making women feel bloated and slightly heavier, without changing their body fat percentage.
Some doctors argue that women do not gain weight on birth control, but if they believe birth control causes weight gain, then they gain weight, and later they attribute this to the birth control rather than to anything else.
From young adulthood into middle age, Americans gain an average of 1 to 2 pounds per year. These are women's prime childbearing years, too, and the time when they are most likely to use birth control implants and other hormonal contraceptives. So, gaining wait through age coincides with birth control use.
Does birth control cause weight gain?
The 2014 Cochrane study quoted earlier in this article did not directly evaluate implants, but it did look at pills and patches, containing the same hormones as birth control implants. It strongly suggests that women are unlikely to gain weight from using birth control implants.
A study published in 2017 looked at weight loss in overweight and obese women after giving birth. One group received a birth control implant, and the other group used birth control that did not use hormones. Slightly fewer implant users had lost weight 6 months into the study. However, the difference in weight loss between the two groups was no statistically significant. This is evidence that hormonal implants probably do not cause weight gain. Even if they do, the gain is minimal.
However, other studies contradict the findings of these two studies.
The 2015 study mentioned early compared 75 users of the implant to 75 users of a non-hormonal IUD. Implant users had modest increases in body size and a 2 percent increase in body fat.
A 2016 study found that the hormonal birth control implant did not directly cause weight gain. However, women who were told that the implant might cause weight gain were more likely to think they had gained weight. In some cases, this caused them to stop using the implant.
A 2015 study arrived at a similar result to this last example. It concluded that teens who used hormonal birth control, including the implant, were likely to perceive weight gain.
In summary, this research means that most women should not notice weight gain when they use the implant, and if they do gain weight, the weight is likely to be minimal.
However, women who think they will gain weight may believe they have gained weight. They may even attribute weight gain due to changes in lifestyle to the implant. This could be a barrier to them making healthy lifestyle changes.
Other implant side effects
Side effects of the birth control implant may include headaches, breast pain, and nausea.
Image credit: Vera de Kok, 2015
Side effects vary from woman to woman and can change based on lifestyle and overall health. Some other side effects of birth control implants include:
- issues with milk supply when breastfeeding
- breast pain
- bleeding between periods, for the first few months of use
- ovarian cysts
- pain where the implant was fitted
- an infection where the implant was fitted
- depression or mood swings
Birth control implants are safe, but some women should avoid them. Women should talk to a doctor about alternatives to the implant if:
- they have a history of blood clots
- they are pregnant or think they might be
- they are allergic to any of the ingredients
- they have progesterone-sensitive cancer, such as breast cancer
- they have liver disease or a liver tumor
- they have a history of unexplained vaginal bleeding
Women with the following health issues will still be able to use the implant safely:
- high blood pressure
- heart disease
- high cholesterol
- kidney disease
- other chronic health conditions
Certain lifestyle factors, such as smoking or being overweight, may exacerbate some risks of the implant. Women should be honest about their lifestyle and health history and should ask their doctors about the risks and benefits of each birth control option.
When to see a doctor
Seek emergency medical care for signs of a blood clot, such as swelling in the leg or unexplained leg pain accompanied by a rapid heart rate. Women who suddenly gain significant weight or retain water should talk immediately to their doctors.
For most women, weight gain is a fact of life, particularly without an aggressive exercise routine and careful management of diet. It is normal to gain a few pounds with each passing year, and weight gain that appears related to birth control implants might be part of normal weight gain that comes with age. Increasing activity can counteract weight gain that accompanies aging.
Women should discuss with their doctors whether their weight gain is healthy and normal, as well as how they can minimize problematic weight gain. For most implant users, weight gain is unlikely. Even if it occurs, it may only be a few pounds.