THE effects of the male equivalent of the Pill should be easily reversible, a study shows.

The contraceptive will never be widely used unless men can be sure that once they stop taking it their sperm counts will return to normal. To test that this is true of the combinations of implants and pills used so far in trials, a team led by Peter Liu, of the Los Angeles Biomedical Research Institute, examined 30 studies on the male Pill published between 1990 and 2005.

The trials have shown that it is possible to reduce the male sperm count to “infertile” levels by using hormone treatments, either in the form of pills, implants, or both. Two trials are in progress, one in China and one in Europe, to prove that the technology works and is safe. But the new study, published in The Lancet, aimed to show that the effects were reversible.

The conclusion was that, in the studies examined, sperm counts returned to a level of 20 million per millilitre — a fertile level — in three to four months.Older men, those of Asian origin, those who had higher sperm counts to start with, and those who took shorter-acting treatments, recovered fertility more quickly. But the trials show that all men will recover fertility — if they had it to start with — if they are prepared to wait long enough.

“Our data provides strong assurance that the previously described efficacy of hormonal male contraceptives is coupled with highly predictable recovery to semen characteristics that are compatible with fertility,” the team concluded.

They offer a few caveats. Few men of Hispanic or African origin were included in the trials, and the threshold of 20 million sperm per millilitre is an arbitrary one. Despite this, their conclusion is optimistic.

Whether this will accelerate the marketing of a male Pill or implants is uncertain. Drug companies may be unwilling to take on the risks of marketing powerful hormonal treatments in an age of litigation.

The combinations so far tried include implants of the male sex hormone testosterone and injections of progesterone, or the other way around. The progesterone — a female sex hornmone — cuts sperm production to low levels, while the testosterone sustains levels of the male hormone.

The unanswered question is whether men will be willing to use the contraceptive. It is unlikely to appeal to any but those in stable, long-term relationships, and women may still want to provide their own independent protection. Also, a male Pill could increase the spread of sexually transmitted diseases by reducing the use of condoms.

The Pill, introduced in more innocent times, might now find the barriers to a licence difficult to surmount.

When millions of healthy people are expected to take a treatment for years on end, even tiny side-effects loom large, as the Pill scares have shown. That the effects of the male Pill are reversible may be important, but not conclusive, in determining its future.

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