Effects of an implant of nomegestrol acetate, a 19-nor-progesterone derivative, on thyroid function

This study was undertaken to assess tri-iodothyronine (T-3), thyroxine (T-4), thyroid stimulating hormone (TSH), T-3 uptake, free T-3 and free T-4 in nomegestrol acetate implant (Uniplant) users. A total of eighteen volunteers of reproductive age who wanted to avoid conception were enrolled in the study. All subjects were investigated before starting treatment. Blood samples for hormonal analysis were taken prior to insertion of the implant. Thereafter, blood samples were drawn at 3, 6, 12, 18 and 24 months of Uniplant use. All subjects had used non-hormonal contraceptives for at least 6 months prior to insertion of the implant. The results observed in this study showed that there was no significant difference in tri-iodothyronine (T-3), thyroxine (T-4) and thyroid stimulating hormone (TSH) during two years of Uniplant use. No significant difference was found in free T-3 levels during two years of Uniplant use. A significant decrease was observed in T-3 uptake (p<0.05) in month 24 and in free T-4 (p<0.05) in month 3 of Uniplant use. All changes observed in this study were inconsistent and all levels were within the normal range.