Nexplanon is a small, flexible birth control rod made primarily of a plastic called ethylene vinyl acetate (EVA) copolymer. The implant is 4 cm long (about 1.6 inches) and 2 mm in diameter, roughly the size of a matchstick, and it contains a synthetic hormone, a substance that makes it visible on imaging, and a tiny amount of a processing agent.
The Plastic That Holds It Together
The body of the implant is built entirely from EVA copolymer, a soft, flexible plastic widely used in medical devices. Nexplanon has two distinct layers of this material: an inner core and an outer skin. The core holds the active ingredients, while the outer skin acts as a membrane that controls how quickly the hormone passes through and enters your body. The EVA used in Nexplanon contains 28% vinyl acetate, which affects the material’s flexibility and permeability. In total, the plastic portion of the rod weighs about 43 mg.
EVA does not contain latex or silicone, which is relevant if you have allergies to either of those materials. It’s the same family of plastic found in some shoe soles, foam padding, and other implantable medical devices.
The Hormone Inside
Each Nexplanon rod contains 68 mg of etonogestrel, a synthetic form of progestin. This is the ingredient that actually prevents pregnancy. It works by stopping ovulation and thickening cervical mucus so sperm can’t easily reach an egg. The hormone doesn’t release all at once. Instead, it slowly diffuses through the EVA skin over the life of the implant, delivering a small, steady dose each day for up to three years. Release rates are highest in the first weeks after insertion and taper gradually over time.
What Makes It Show Up on X-Rays
Nexplanon contains 15 mg of barium sulfate mixed into the core alongside the hormone. Barium sulfate is a dense, white compound commonly used in medical imaging. It’s what makes Nexplanon “radiopaque,” meaning a healthcare provider can locate the implant using a standard X-ray, CT scan, or ultrasound if needed.
This was actually the key material change from Nexplanon’s predecessor, Implanon, which the FDA approved in 2006. Implanon used the same EVA plastic and the same hormone but did not contain barium sulfate. That made it difficult to locate if the rod migrated or was inserted too deeply. When Nexplanon replaced Implanon in 2011, the addition of barium sulfate solved that problem.
The Processing Agent
The implant also contains a very small amount of magnesium stearate, just 0.1 mg. This is a common additive used during manufacturing to prevent ingredients from sticking to equipment. You’ll find it in countless pills and supplements. It plays no active role once the implant is in your body.
Full Ingredient Breakdown
- EVA copolymer (28% vinyl acetate): 43 mg, forms the rod’s core and outer skin
- Etonogestrel: 68 mg, the synthetic progestin hormone that prevents pregnancy
- Barium sulfate: 15 mg, makes the implant visible on X-rays and CT scans
- Magnesium stearate: 0.1 mg, a manufacturing aid
Why the Materials Matter
The design is intentionally simple. A single rod, one hormone, one type of plastic. The EVA copolymer is biocompatible, meaning your body tolerates it without breaking it down or rejecting it. The rod stays intact for the full three years and is removed in one piece. It doesn’t dissolve, and the plastic doesn’t degrade inside your arm.
The two-layer EVA structure is what gives Nexplanon its steady, long-lasting hormone delivery. If the hormone were simply packed into a rod without the outer membrane, it would release too quickly and lose effectiveness well before three years. The skin layer slows diffusion to a controlled rate, which is why the implant can work reliably over such a long period with just 68 mg of hormone total.
If you’re concerned about a specific material sensitivity, the complete ingredient list above covers everything in the implant. There are no metals, no silicone, no latex, and no natural rubber components.