Gains Reported in Test of Male Contraceptive
Researchers have shown for the first time that a male contraceptive that works like the female birth control pill can be highly effective in preventing pregnancy.
In a one-year study, a World Health Organization task force found that weekly injections of testosterone enanthate, a synthetic variant of a naturally occurring male hormone, “can maintain safe, stable, and effective, and reversible contraception.”
There was one pregnancy among the 157 fertile couples who used continuing testosterone injections as their only form of birth control for up to a year, according to a report in today’s issue of The Lancet, a British medical journal.
This failure rate is lower than typical one-year failure rates for birth control pills (3 per 100) and condoms (12 per 100).
The preliminary success opens the door for researchers to develop a male contraceptive that is suitable for widespread use, such as a longer-acting hormone injection that can work for three to four months.
“We are testing a concept. This will not necessarily be the final product,” said Dr. C. Alvin Paulsen, one of the study’s lead researchers and a professor of medicine at the University of Washington.
One popular possibility, a testosterone birth control pill, appears very unlikely “in the foreseeable future” because it carries an unacceptable risk of liver damage, Paulsen said. A higher concentration of testosterone reaches the liver when taken by mouth than when injected.
Currently, condoms, vasectomies and abstinence are the only forms of birth control available to men. Earlier this year, the U.S. National Research Council, citing a dearth of effective birth control methods to meet varying medical and social needs, called for a marked increase in the number and types of contraceptives for both men and women.
Researchers have known for years that repeated male hormone injections can cause a reversible condition in which men can ejaculate semen, but produce little or no sperm. In a manner similar to the female birth control pill, testosterone injections trick a man’s body into shutting off the normal biochemical signals from the brain that direct the testes to produce sperm.
The new study represents the first formal test to determine if the hormone injections are an effective contraceptive. Previous studies only measured sperm counts, and couples used additional contraception.
“This is a study that should have been done a long time ago. . . . But it is better late than never,” said Dr. Gabriel Bialy, chief of the contraceptive development branch at the National Institute of Child Health and Human Development in Bethesda, Md.
A major drawback of the current regimen is the frequency of the injections. Another is the failure to reduce the sperm count to zero in about 35% of the men studied, Bialy said.
The WHO task force acknowledged the “obvious impracticality” of weekly injections but maintained that the first test had to be conducted with a hormonal regimen known to be safe and reversible.
Side effects included weight gain--an average of six pounds--and acne, Paulsen said. There were no changes in potency or sex drive. The long-term potential hazards from testosterone injections include heart and prostate disease.
While it only takes one sperm to fertilize an egg, most fertile men have a great excess of sperm. A normal male sperm count ranges from 20 million to 150 million sperm per milliliter of semen.
The male contraceptive study initially involved 271 healthy fertile men from seven countries, including four dozen couples from the Seattle area, and couples from China, Australia and France.
The researchers identified the men whose sperm counts dropped to zero after the weekly 200-milligram injections, as measured by the examination of semen specimens under a microscope once every two weeks. A total of 114 men withdrew from the study for a variety of reasons, including 68 whose sperm counts did not drop to zero within six months.
After the hormone injections began, it took an average of four months for the men’s sperm counts to drop to zero. When this was achieved, the men and their sexual partners abandoned other means of contraception.
After the hormone injections were stopped, it took an average of 3.7 months for sperm counts to return to normal. Some men still have mild decreases in sperm counts, but follow-up data is incomplete, the report said. To date, 10 pregnancies have been recorded during the recovery phase.
The WHO task force is now studying several hundred men whose sperm counts drop to low levels--5 million sperm per milliliter or less--after testosterone injections, but not to zero.
Male contraception researchers are hopeful of a similar success with such men. It would greatly increase the number who might benefit and “provide the necessary impetus to create compounds where the injections can be postponed to every three or four months,” Paulsen said.
Such a longer-acting preparation might be a different form of testosterone, analogous to injectable female contraceptives. Depo-Provera and other such injectable contraceptives are available in Western Europe and some Third World nations, but not in the United States. Preliminary tests of this approach may begin in Germany next year, Paulsen said.
Another possibility, according to Bialy and Paulsen, are injections of both testosterone and a drug known as an LHRH antagonist, which shuts off almost all the normal hormonal stimuli to the male sex organs. Preliminary tests of this approach are under way at the University of Washington, Vanderbilt University in Nashville, and in Western Europe.
NEXT STEP
Despite the research success with an injectable male contraceptive, researchers say not to expect it in pharmacies any time soon. The prototype approach, which requires weekly injections of the male hormone testosterone, is not considered practical. Refining the approach by developing a longer-action injection may take 5 to 10 years or longer.
