Progestagen-only oral contraceptives: comparison of the metabolic effects of levonorgestrel and norethisterone.

A 6-month single-blind study compared the use of a progestagen-only oral contraceptive containing norethisterone 350 micrograms/day (NE 350) with one containing levonorgestrel 30 micrograms (LN 30), to assess the metabolic effects. At the end of 6 months, there were no significant differences between the two groups with respect to plasma cholesterol, lipoproteins including HDL subfractions, triglycerides or glucose concentration. Levels of fibrinogen, plasminogen, Factor VII, Factor X and antithrombin III were also similar. Women changing from a combined oral contraceptive to LN 30 showed a significant fall in Factor X. Mean blood pressure fell on LN 30 by 7/9 mmHg, but the 6-month reading did not differ significantly from that in women on NE 350. Acceptability, and the metabolic effects of the two preparations were similar in this study. Further larger studies are warranted.