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British Journal of Family Planning. 1990 Jan; 15(4 Suppl):27-9.The long-acting injectable contraceptives, once-a-month injectables, vaginal rings, and implants, either in use or being clinically tested, are reviewed briefly. About 6 million women now use injectables, 4 million use Depo-Provera, and 1 million use norethisterone enanthate (NET-EN) in a once-monthly schedule. Other once-monthly injectables are being developed by WHO, such as a dihydroxy-progesterone acetophenide-estradiol enanthate being tested in Mexico. These injections are highly effective and acceptable, despite frequency, because they cause regular withdrawal bleeding. Other combinations already tested by WHO are HRP 102 (norethisterone enanthate 50 mg-estradiol valerate 5 mg), and HRP 112 (depo-medroxyprogesterone acetate 25 mg-estradiol cypionate 5 mg). Continuation rates for these methods were 64.5 and 63.2%. Lower doses were not as effective in cycle control. Depo-Provera (depo- medroxyprogesterone acetate, DMPA) is available in 85 countries, and accounts for 65% of injectables, while NET-EN is available in over 40 countries and makes up 15%. Recent studies with DMPA have shown that efficacy can be affected by variations in particle size of the microcrystals, as well as by the population using it. Vaginal rings containing levonorgestrel have reached Phase II trials; failures have been reported due to inconsistent quality. Besides the well-known Norplant, an implant called Capronor is being developed. It is a polycaprolactone tube 4 cm long containing levonorgestrel in ethyl oleate vehicle. IT has a zero order release and biodegrades after 2 years.