Active Ingredient: The Hormone Etonogestrel
At the core of the Nexplanon implant's contraceptive power is its active ingredient: etonogestrel. Each implant contains 68 milligrams (mg) of this synthetic progestin, a hormone similar to the progesterone produced naturally in the female body. Unlike combination contraceptives that contain both estrogen and progestin, Nexplanon is a progestin-only method.
Once the matchstick-sized implant is inserted just under the skin of the upper arm, it begins to release a continuous, low dose of etonogestrel into the bloodstream. The rate of release is not static but gradually decreases over time, while remaining at therapeutic levels to prevent pregnancy.
- Initial release rate: Approximately 60-70 micrograms (mcg) per day during the first 5-6 weeks.
- Release rate by year 1: Decreases to about 35-45 mcg per day.
- Release rate by year 3: Tapers to approximately 25-30 mcg per day.
This steady hormone delivery is a key factor in its high efficacy, as it eliminates the possibility of human error associated with daily pills.
How Etonogestrel Prevents Pregnancy
Etonogestrel prevents pregnancy through multiple mechanisms working together.
- Inhibits Ovulation: The primary function of the hormone is to suppress the release of an egg from the ovaries, a process known as ovulation. Without an egg to fertilize, pregnancy cannot occur.
- Thickens Cervical Mucus: The hormone causes the mucus in the cervix to become thicker and more hostile to sperm. This creates a barrier that prevents sperm from traveling into the uterus to reach an egg.
- Thins Uterine Lining: Etonogestrel also changes the lining of the uterus, making it difficult for a fertilized egg to implant.
The Physical Structure: Copolymer and Barium Sulfate
Beyond the active hormone, the physical structure of the Nexplanon implant is crucial to its function. The implant is a flexible, white or off-white rod, approximately 4 cm long and 2 mm in diameter.
- Polymer Material: The rod is made from a non-biodegradable material called ethylene vinyl acetate (EVA) copolymer. The EVA copolymer serves as the matrix that holds the etonogestrel and controls its slow, consistent release over the three-year period.
- Radiopaque Marker: A key component differentiating Nexplanon from its predecessor, Implanon, is the inclusion of 15 mg of barium sulfate. This makes the implant radiopaque, meaning it is visible on x-ray imaging. The radiopaque property is a critical safety feature, allowing healthcare professionals to confirm the implant's proper placement or locate it if it has migrated or is difficult to palpate.
- Other Ingredients: Some formulations of the implant may also include a small amount of magnesium stearate, a common pharmaceutical additive.
Comparing Nexplanon and Implanon
While both implants use etonogestrel as the active hormone, there are key distinctions between Nexplanon and the earlier version, Implanon.
| Feature | Nexplanon | Implanon |
|---|---|---|
| Active Ingredient | Etonogestrel (68 mg) | Etonogestrel (68 mg) |
| Active Life | Up to 3 years | Up to 3 years |
| Radiopaque | Yes (contains barium sulfate) | No |
| X-Ray Visibility | Visible on x-ray imaging | Not visible on x-ray |
| Insertion Device | Uses an improved preloaded applicator | Used a previous inserter |
| Localization | Easily located with x-ray | Relied on palpation and other imaging |
The Application and Safe Usage
For insertion and removal, Nexplanon is preloaded into a sterile, disposable applicator designed to facilitate correct subdermal placement. This is done by a trained healthcare professional, ensuring the implant is correctly positioned just beneath the skin of the upper, non-dominant arm. Following insertion, the provider confirms the implant's presence by palpation and, if necessary, x-ray, thanks to the barium sulfate. A pressure bandage is applied to minimize bruising.
After three years, the implant must be removed. Removal is performed by a healthcare professional in a similar procedure, requiring a small incision. Once removed, a new implant can be inserted, or the patient can resume fertility immediately.
Conclusion: A Blend of Simplicity and Advanced Technology
What is in a Nexplanon implant is a carefully engineered blend of a time-tested synthetic hormone and advanced delivery materials designed for long-term contraception. The etonogestrel provides the contraceptive effect, while the non-biodegradable EVA copolymer ensures a sustained, low-dose release over three years. The inclusion of barium sulfate adds a crucial layer of safety by making the device visible on x-ray, making both proper placement and removal more secure. This combination makes Nexplanon one of the most effective and user-friendly reversible contraceptives available. For more information, consult the official FDA label for Nexplanon (etonogestrel implant) Radiopaque.
