Contraceptive implants are a form of long-term reversible birth control. Like other forms of hormonal birth control, the implant may cause side effects, including unexpected weight changes.

Research on whether the implant directly or indirectly causes weight gain is mixed. It’s unclear whether this is due to the implant or other lifestyle habits.

Keep reading to learn why you may gain weight and other potential side effects of the implant.

Understanding how the implant works is essential to understanding its side effects.

The birth control implant is available in the United States as the brand name Nexplanon.

Your doctor will insert this implant into your arm. Once properly placed, it will release the synthetic hormone etonogestrel into your bloodstream for several years.

This hormone imitates progesterone. Progesterone is a natural hormone that regulates your menstrual cycle and the hormone estrogen.

This additional etonogestrel disturbs your body’s natural hormonal balance, which can contribute to weight gain.

Although weight gain is recognized as a potential side effect of the implant, researchers are unclear whether the two are related.

To date, no evidence suggests that the implant itself causes weight gain. Many studies have concluded the opposite.

For example, a 2016 study concluded that people using the implant didn’t gain weight, though they felt they had. The researchers thought people might have perceived this weight gain because they knew of this possible side effect.

Other research from 2016 looked at progestin-only contraceptives, including the implant. Researchers found there wasn’t much evidence of weight gain for these types of contraceptives.

The researchers recommended that people be counseled to understand weight gain better so they don’t discontinue using these forms of birth control.

Both studies state that people may perceive that they’re gaining weight with the implant, even though it isn’t increasing their weight.

More recent research, including a 2019 research review, concluded that long-term use did not lead to significant weight gain.

However, a 2020 study suggests that there could be a genetic component. Variations in the estrogen receptor 1 (ESR1) gene could influence any weight gained from implant use.

The authors also found that people with a higher body mass index (BMI) were more likely to gain weight from an implant.

Weight gain can also be caused by other factors, such as aging, a sedentary lifestyle, eating habits, or an underlying medical condition.

Remember: Weight gain is an individual experience for each person using the implant. Studies that discuss the “average user” may not reflect your body’s reactions to the contraceptive.

In addition to weight gain, you may experience other side effects with the implant.

After the implant is placed, you may temporarily have:

  • arm pain
  • bruising at the insertion site
  • dizziness
  • nausea

Other side effects may resolve after a couple of months. These include:

  • acne
  • back pain
  • breast pain
  • fatigue
  • headache
  • irregular menstrual cycles
  • painful menstrual periods
  • shifts in mood
  • spotting between menstrual periods
  • stomach pain
  • vaginal inflammation (vaginitis)

Consult a doctor or another healthcare professional if you experience discomfort at the injection site or develop sudden and painful headaches. They can determine the underlying cause and advise you on any next steps.

You should also make an appointment with a healthcare professional if you experience any side effects that cause distress or disrupt your daily life.

The implant may not be the best contraceptive for everyone. If it’s not right for you, a healthcare professional can recommend a more suitable alternative.