NEW YORK (Reuters Health) – Mifepristone, a pregnancy-terminating agent, can inhibit ovulation and induce amenorrhea and could, therefore, represent a novel estrogen-free oral contraceptive agent, according to a recent report.
While estrogen-containing agents effectively prevent pregnancy, their use has been tied to adverse events such as venous thromboembolism. Progestogen-only pills have a relatively high failure rate and can produce functional cysts. Thus, the need has emerged for oral agents that contain neither hormone.
Dr. David T. Baird, from the University of Edinburgh in the UK, and colleagues assessed the pregnancy-related outcomes of 90 healthy women who were randomized to receive 2 or 5 mg of mifepristone for 120 days. Fifty of the women were from Edinburgh, while the remainder came from Shanghai.
Treatment with either dose of mifepristone was associated with inhibition of ovulation and induction of amenorrhea in most women, the authors note. The 5-mg dose was associated with fewer ovulatory episodes than the 2-mg dose, and it produced a more predictable pattern of amenorrhea.
In women from Edinburgh, mifepristone appeared to cause an increase in endometrial thickness, while just the opposite was observed in Chinese women. Histologic analysis revealed no evidence of hyperplasia, only atrophic or cystic changes.
Fifty women were sexually active and used no other method of contraception, the researchers note in the January issue of The Journal of Clinical Endocrinology and Metabolism. None of these women became pregnant.
While the findings are encouraging, the authors note that "it is not possible to assess the contraceptive efficacy accurately from these preliminary data, particularly because the majority of women exposed to the risk of pregnancy were Chinese in whom ovarian activity was suppressed more effectively than in women in Edinburgh." Longer-term studies are needed to establish the safety and efficacy of mifepristone, they add.