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Levonorgestrel implants, sold under the brandnames Norplant among others, is a type of contraceptive implant for birth control. It was developed by Sheldon J. Segal and Horatio B. Croxatto at the Population Council beginning in 1966, with the first clinical trial in Chile in 1974. It was first approved in Finland on November 23, 1983, where it was manufactured by Leiras Oy Pharmaceuticals. The original Norplant consisted of a set of six small (2.4 mm × 34 mm) silicone capsules, each filled with 36 mg of levonorgestrel (a progestin used in many birth control pills) implanted subdermally in the upper arm and effective for five years. The original (six capsule) Norplant's production has been phased out; USAID's contract ran until December 2006. The original (six capsule) Norplant was approved by the U.S. Food and Drug Administration (FDA) on December 10, 1990, and marketed in the United States in 1991 by Wyeth Pharmaceuticals. Norplant distribution in the United States ended in 2002; limited supplies still remained in the U.S. until 2004. Norplant was withdrawn from the UK market in 1999. Production of Norplant was discontinued globally in 2008.〔 〕 Norplant II (Norplant-2, Jadelle), also developed by the Population Council and manufactured by Schering Oy, consists of two small (2.5 mm × 43 mm) silicone rods each containing 75 mg of levonorgestrel in a polymer matrix, instead of six capsules. It was approved May 31, 1996 by the FDA as being effective for three years; it was subsequently approved November 22, 2002 by the FDA as being effective for five years. Jadelle has not been marketed in the United States; Jadelle is the successor to the original Norplant in USAID's contract beginning January 2007. == Medical uses == Norplant is 99%99.95% effective at preventing pregnancy, and is one of the most reliable, though not the most available, forms of birth control. Norplant prevents pregnancy through multiple methods: by preventing ovulation, which means that no eggs are released for fertilization; by thickening the mucus of the cervix, which prevents sperm from entering; and by thinning the lining of the uterus, which makes implantation of an embryo less likely. The way in which Norplant causes these effects is by use of hormones. A small amount of the hormone progestin is released through the capsules continuously, more during the first year and a half, but then at a level similar to most contraceptive pills afterward. Like all hormonal contraception, Norplant does not protect against sexually transmitted infections. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Levonorgestrel implant」の詳細全文を読む スポンサード リンク
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