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Contraception Report. 1999 Jan; 9(6): p..A recent WHO-sponsored study has demonstrated that the progestin levonorgestrel, used alone, is a highly effective and well-tolerated form of emergency contraception. With the proportion of pregnancies prevented up to 95% - depending on the timeliness of administration - the levonorgestrel regimen proved more effective than the most commonly used regimen, the Yuzpe method. The Yuzpe method employs a dual-hormone (ethinyl estradiol plus levonorgestrel) approach to preventing pregnancy. Despite the Yuzpe regimen's 75% efficacy rate (a weighted average from 10 studies) the method has been associated with drawbacks. About 50% of users experience nausea and 20% report vomiting, which can reduce patient compliance. (excerpt)
Randomised controlled trial of levonorgestrel versus the Yuzpe regimen of combined oral contraceptives for emergency contraception.
Lancet. 1998 Aug 8; 352(9126):428-33.A previous study suggested that provision of two 0.75 mg doses of levonorgestrel for emergency contraception caused less nausea and vomiting and was more effective than the Yuzpe regimen of combined oral contraceptives (two doses of 100 mcg of ethinyl estradiol and 0.5 mg of levonorgestrel). These two regimens were evaluated further in a double-blind, randomized World Health Organization study of 1998 women recruited from 21 centers worldwide who requested emergency contraception within 72 hours of unprotected intercourse. Among the 1955 women for whom the outcome was known, the crude pregnancy rate was 1.1% (11/976) in the levonorgestrel group and 3.2% (31/979) in the Yuzpe group. The crude relative risk of pregnancy for levonorgestrel compared with the Yuzpe regimen was 0.36 (95% confidence interval, 0.18-0.70). The proportion of pregnancies prevented was 85% in the former group and 57% in the latter group. Nausea and vomiting occurred significantly less frequently in the levonorgestrel group (23.1% and 5.6%, respectively) than in the Yuzpe regimen group (50.5% and 18.8%, respectively). The efficacy of both treatments declined significantly (p = 0.01) with increasing time since unprotected intercourse. These findings confirm that the levonorgestrel regimen may be more effective and is better tolerated than the current standard in emergency contraception.
Contraception. 1982 Mar; 25(3):231-41.A randomized, controlled, clinical trial comparing 6 combined oral contraceptives (OCs) with 50 mcg or less of ethinyl estradiol was undertaken in 10 WHO Collaborating Centers for Clinical Research in Human Reproduction. A total of 2430 women entered the trial and were observed for 28,077 woman-cycles. All low-dose combined OCs demonstrated equivalent efficacy with 1-year pregnancy rates of 1-6%. However, discontinuation rates for medical reasons differed significantly between the treatment groups with the preparation containing 20 mcg ethinyl estradiol and that containing 400 mcg norethisterone acetate being associated with higher discontinuation rates due to bleeding disturbances. Even among the preparations which did not differ in discontinuation rates, the reasons for discontinuation did differ. Women receiving norethisterone preparations tended to discontinue because of bleeding disturbances while those receiving the levonorgestrel-containing preparations tended to discontinue because of complaints of nausea and vomiting. (author's)