Male contraception: an overview of the potential target events

The contraceptive options available to men have not changed in several decades and are still limited to the non-surgical methods of the use of a condom, a timely withdrawal, or a surgical procedure that removes a segment of the vas deferens (vasectomy). The first two approaches have relatively higher failure rates whereas the last approach is largely irreversible and may not be suitable for younger men. Thus, providing a safe, effective and readily available contraception for men has remained an unfulfilled goal. In this article, we intend to review the current status of the research and development on male contraceptives. It is apparent that the scientific community in the past few decades has witnessed impressive progress in understanding the basics of male physiology, the knowledge necessary for developing new contraceptive methods for men. We will highlight various new and improved strategies for the regulation of fertility in males. The diverse approaches that are at various stages of development and/or in clinical trials include: 1) administration of hormones, herbal extracts or chemicals to suppress/arrest sperm production in the testes (spermatogenesis); 2) interference with the delivery of spermatozoa during ejaculation by targeted blockage of vas deferens with plugs or chemicals (polymers) that prevent flow of sperm through the vas duct; 3) active or passive immunization of males with well characterized antigens/antibodies which are intended to block sperm function; and 4) administration of site-directed antagonists to block specific sperm function(s) necessary for normal fertilization. All these approaches do not involve surgery and are reversible. Our intention is to discuss the current status of various approaches which show promising results in clinical trials, particularly in China and India, the world's most populous nations.