NORPLANT: levonorgestrel-releasing contraceptive implant.

NORPLANT is the newest contraceptive system to be introduced world-wide, with nearly a million current users. It consists of six Silastic capsules containing levonorgestrel (LNg), which are inserted under the skin in the arm. Release of the steroid commences immediately so that, after several weeks, circulating levels of LNg stabilize between 0.3 and 0.4 ng/ml of plasma, and they persist elevated with a minor decline for over 5 years. The gross cumulative pregnancy rate at 5 years is 2.6 per 100 woman-years. In the majority of women it produces no abnormalities in a variety of clinical chemistry, metabolic, haematological and coagulation parameters. The most common side-effect is disruption of the menstrual bleeding pattern; this is reported by two-thirds of the users in the first months and by one-third by the fifth year. Because it is the most disturbing side-effect for many users, counselling prior to insertion is of paramount importance. NORPLANT exerts varying degrees of gonadotrophin and ovarian inhibition, including anovulation and luteal insufficiency. Endometrial development is irregular and, irrespective of oestrogen levels, cervical mucus is thick and scanty at all times due to the strong antioestrogenic effect of LNg. Inhibition of sperm penetration fully accounts for the antifertility effect of NORPLANT in ovulatory cycles. The high contraceptive efficacy, lack of serious side-effects, reversibility and the convenience of long-term unattended use explain the high acceptability of NORPLANT.