New Vision (Kampala) - December 16, 2006

There are several at various stages of development, with the latest a single-dose pill that produces a "dry orgasm", the slightly eye-watering notion that the man experiences sexual pleasure, but does not produce any semen.

Is this the end of the condom? Unfortunately not. Apart from the risk of sexually transmitted diseases from a casual partner, the pill does not offer spur-of-the-moment temporary infertility on demand. It takes around five hours to take effect, which might take some of the spontaneity out of a one-night stand. And how many women are going to believe: "I took the male pill before leaving for the pub tonight"?

More likely is that all the male pills in development, including this "instant" one, which is unlikely to be available for at least another five years, will be used by men in long-term relationships with women who can't, or would prefer not to, use the female contraceptive pill.

Researchers Nnaemeka Amobi and Christopher Smith, both physiologists at King's College London, have been developing the dry orgasm approach for 17 years, but are only now at the stage of talking to a drug company about taking their experimental drugs to the next stage of safety testing on animals.

They set off on their search for a male pill after reading a report by Israeli researchers about a treatment for high blood pressure called phenoxybenzamine. In a test on people, the drug had the side-effect of temporarily preventing ejaculations in males, and another drug used to treat schizophrenia (thioridazine) had a similar effect. "No one knew how they produced that effect," says Amobi.

Both drugs act in the same way. They interfere with muscles in the vas deferens, the tube leading from the testes. Under normal conditions, rhythmic movement of muscles running lengthways along the vas deferens and circular rings of muscle around the tube propel sperm during an ejaculation. But the two drugs have the side-effect of shutting down the lengthways muscles. "They relax it," says Amobi. That means the sperm don't go anywhere. Usefully, the effect wears off 12 to 24 hours after taking the pills.

Perfect then for a male contraceptive - except both drugs have unhelpful side effects. The schizophrenia drug causes drowsiness and the blood pressure pill can cause dizziness. Amobi and Smith had to start from scratch, finding other compounds that have the same effect on ejaculation without affecting other muscles (a male pill that also shuts down muscles that move food through the gut would be a non-starter, for example).

By experimenting on samples of human vas deferens cut out during vasectomy operations, Amobi says that the pair have identified a collection of chemical compounds that work in the same way. The next stage will be to test the chemicals in animals, although it is not yet clear which species.

The vas deferens of rats - often the animal of choice for initial drug tests - is too different to yield meaningful results. Amobi says he will not be using monkeys.

Although it has taken nearly two decades to get this far, the test drugs that Amobi and Smith have developed are still a long shot. Only about one in 250 chemicals that begin testing in animals make it to the pharmacy.

Other experimental male pills have made it further along the road to being approved as medicines. Adjudin has passed through experiments in animals, but has yet to be tested in humans.

It prevents developing sperm cells from linking up with nurse cells in the testes. So the idea is that although the man ejaculates, his sperm are not fully developed and so not capable of fertilising an egg.

But the approach furthest down the line is based on a concoction of hormones. This is not delivered as a pill, but as an injection or an implant - and there are hormone-related side-effects.

"The clinical trials (in volunteers) show that it works, but a lot of men complain about the injection," says Amobi.

So it appears that the days of the male head-in-the-sand attitude to contraception are coming to an end.

But, regardless of whether it comes as a pill, an injection or a one-dose "instant pill", the advent of male contraceptives will not affect casual sexual encounters. The drunken fumble with the condom wrapper will still be the bane of the one-night stand.

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