In August 2000, Wyeth suspended shipments of Norplant in the United States because during regular quality assurance monitoring, representative samples of seven lots distributed beginning October 20, 1999 tested within product specifications, but at the lower end of the release rate specification for shelf life stability, raising concerns about those lots' contraceptive effectiveness. Wyeth recommended that women who had Norplant capsules from those lots implanted use backup contraception until they determined the clinical relevance of the atypically low levels of levonorgestrel release.