(HealthDay News) – Obese women who receive a contraceptive implant have lower drug levels in the six months following implant insertion compared with normal-weight women, according to a study published in the August issue of the American Journal of Obstetrics & Gynecology.

Sara Mornar, DO, from the University of Chicago, and colleagues assessed the pharmacokinetics of an etonogestrel contraceptive implant in 13 obese African-American women (body mass index of ≥30kg/m²) and four normal-weight white women (body mass index of <25 kg/m²). After insertion, plasma etonogestrel levels were measured every 50 hours, though 300 hours, then at three months and six months.

The researchers found that etonogestrel levels were consistently lower in the obese women and 31%–63% lower than the normal-weight women, though the differences did not reach statistical significance. Peak plasma levels were achieved at 150 hours post insertion. There were no serious adverse events and obese women rated the implant as highly acceptable.

“Obese women have lower plasma etonogestrel concentration than normal-weight women in the first six months after implant insertion,” Mornar and colleagues write. “These findings should not be interpreted as decreased contraceptive effectiveness without additional considerations.”

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