Contraceptive implant (Nexplanon)

The contraceptive implant, sold as Nexplanon in the US (Implanon in some other countries), is a small flexible rod about 4cm long placed under the skin of the inner upper arm. It releases the progestin etonogestrel steadily for up to 3 years. Insertion and removal are done in a clinic visit under local anesthesia.

Efficacy is the highest of any reversible contraceptive, above 99.9% in both typical and perfect use, because compliance is removed from the equation entirely.

This is informational, not medical advice. Implant placement and choice should be discussed with a qualified provider.

How it works

Etonogestrel works through three mechanisms, with ovulation suppression as the dominant effect:

  1. Ovulation suppression. The implant produces sustained progestin levels high enough to suppress the LH surge in the large majority of cycles, much more reliably than the mini-pill.
  2. Cervical mucus thickening. Blocks sperm penetration.
  3. Endometrial thinning. Reduces implantation receptivity.

Suppression is robust in years 1 and 2 and may weaken slightly in year 3. After removal, fertility typically returns within a few weeks.

Cycle implications

For cycle syncing, the implant is similar to other progestin-dominant suppression methods. Most users do not ovulate, which means no true follicular phase or luteal phase and no natural progesterone cycle.

The bleeding pattern on the implant is unpredictable and is the main quality-of-life issue users report:

  • Roughly 1 in 5 users has irregular spotting throughout each month.
  • Roughly 1 in 5 stops bleeding entirely.
  • The rest have a mix of light periods, infrequent bleeds, or occasional heavy days.

The bleeding pattern in the first 3 months is a poor predictor of the long-term pattern. Many users who have problematic bleeding early settle into lighter or absent bleeding by month 6.

Common side effects

  • Irregular bleeding (the most common reason for discontinuation).
  • Headaches.
  • Acne, especially in users sensitive to androgenic effects of etonogestrel.
  • Mood changes in a subset of users.
  • Weight gain is reported by some users; the population-level effect is small.
  • Breast tenderness.
  • Ovarian cysts (functional, usually resolving on their own).

Rare but serious: deep implant migration (very rare with Nexplanon, which is radiopaque and easier to locate than older Implanon), insertion-site infection, scarring.

When to consider

  • Want highly effective long-acting reversible contraception without daily compliance.
  • Estrogen is contraindicated.
  • Tolerate or prefer irregular or absent bleeding.
  • Want a method that is easier to start and stop than an IUD (no pelvic insertion).

When NOT to consider

  • Strongly prefer predictable monthly bleeds.
  • History of certain breast cancers.
  • Severe liver disease.
  • Unexplained vaginal bleeding before workup.
  • Strong preference for keeping the natural cycle (consider the copper IUD or fertility awareness).

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