Depression of plasma testosterone levels in men with norethindrone

This preliminary study demonstrates the ability of norethindrone (NET) to depress plasma levels of testosterone (T) in men. A single oral dose of 25 mg of NET had no effect on the T levels despite peak plasma levels of NET of about 80 ng/ml. A daily dose of 25 mg of NET given orally for three weeks resulted in plasma levels of NET of 10–20 ng/ml when measured about 12 hours after the intake of the tablet. After four to five days of this treatment the plasma levels of T had decreased to 1–2 ng/ml, but were not further depressed below this level. After discontinuing the NET treatment, normal plasma levels of T were reached within four to five days. The daily treatment with 25 mg of NET for three weeks followed by 25 mg once a week decreased the total sperm count and increased the percentage of abnormal spermatozoa. The treatment had no effect on libido or potency.