Researchers have reported 99 per cent success rate in Chinese trials on testosterone as male contraception. It is the largest study conducted anywhere in the world.
Hormonal contraception for men has been in clinical stages of development for almost two decades. This approach works by using testosterone or a combination of testosterone and a progestin to suppress sperm production. When testosterone is added to a man's system, testosterone levels are lowered in the testes, resulting in reduced sperm production.
The testosterone injections in the phase III trials were tried on 1,045 healthy and fertile men, aged between aged 20 and 45.
The scientists reported in The Endocrine Society's Journal of Clinical Endocrinology & Metabolism (JCEM):"Hormonal male contraceptive regimens effectively and reversibly suppress sperm production but there are few large-scale efficacy studies. Objective: The safety, contraceptive efficacy, reversibility and feasibility of injectable testosterone undecanoate (TU) in tea seed oil as a hormonal male contraceptive was assessed. Design: This was a mutilcenter, phase III, contraceptive efficacy clinical trial. Participants: 1045 healthy fertile Chinese men were recruited throughout China into the study. Intervention(s): Monthly injections of 500 mg TU, administered for 30 months..."
All of the men who took part in the study had fathered at least one child within the previous two years and none of their partners had fertility problems. During the period of the trial, they could not father a child. But after the study ended all of the men, barring two, saw their fertility levels return to normal.
"For couples who can not, or prefer not to use only female-oriented contraception, options have been limited to vasectomy, condom and withdrawal," said Dr Yi-Qun Gu from the National Research Institute for Family Planning in Beijing.
"Our study shows a male hormonal contraceptive regimen may be a potential, novel and workable alternative."
However, he warned that larger tests were needed to determine the long-term safety of the injections, particularly on men's hearts and prostate glands.
Two earlier trials, sponsored by the WHO, have shown considerable promise. The first study, in seven countries between 1986 and 1990, involved 271 men who received weekly injections of 200 mg of the hormone compound testosterone enanthate.
The second study, in nine countries in 1994, involved 399 men who received testosterone enanthate on the same schedule.
The studies had defined the level to which sperm counts must decline in order to prevent men's partners from becoming pregnant. Also, the second study established that a hormonal contraceptive could be effective—about one pregnancy among the partners of every 100 men per year of use when sperm production is adequately suppressed.
Testosterone undecanoate, used in China, is among the newest and most successful testosterone preparations. It is longer acting than other compounds such as testosterone enanthate, and it allows men to receive injections bimonthly or monthly instead of weekly.
Testosterone by itself does not suppress sperm production in non-Asian men as well as it does in Asian men, and therefore in other regions a male hormonal contraceptive would most likely combine a testosterone with another hormonal compound to improve effectiveness. Studies have been unable to pinpoint the cause for the difference in effectiveness between Asian men and other men.
The two primary challenges remaining for developing other male hormonal contraceptives are the need for frequent injections and the inability to uniformly suppress sperm production in all users. Researchers are looking into longer-acting formulations of testosterone and combined hormonal formulations to overcome these challenges.
Earlier this year scientists said that they were a step closer to developing a male Pill after they identified a rare defective gene which can cause infertility.
Developing a drug which could target healthy versions of the gene could be an effective contraceptive, it is felt.