Aspects of thyroid function during use of Norplant implants

Plasma thyroxin (T4), triiodothyronine (T3), T3-uptake and thyroid stimulating hormone (TSH) were measured in 18 women using Norplant implants or Norplant-2 implants for six months. Free T4-index and free T3-index were also calculated. All women had used non-hormonal contraceptives before insertion of the implants. T4 decreased and T3-uptake increased, indicating a lower level of thyroid binding proteins during treatment. Free T4-index remained unchanged, indicating that the free concentration of thyroxin was unaltered. All women were euthyroid and TSH was unchanged. It is concluded that treatment with Norplant implants does not result in a change in thyroid function.