Press releases in science seem to jump the gun more and more these days. First the groups running the human genome project announce its completion with only 97% of two (conflicting) rough drafts in the bag; now we are told that a male pill, effective and free from side effects, could be with us in five years.

Five years feels like a long time for something that is already a suspicious 35 years behind the female pill - and in fact wasn't it about three years ago that we were told we were about three years away from the male pill being on the market? Why are we still waiting?

The traditional answer is that an ovary making one egg once a month presents a much easier target to hit pharmacologically than a testicle making a thousand sperm a minute. And maybe there is no gender bias - maybe you really do need to get the big guns out for the testicles - which, of course, is every man's fear.

Previous attempts at the male pill have suffered from dismal side effects: impotence, reduced libido, acne, mood swings, high blood pressure and, most terrifyingly, shrinking testicles. If some of these sound similar to the side effects of the female pill, it is because most of them have included similar progesterone based hormones, such as desogestrel, along with (perhaps more reassuringly) testosterone.

There are, of course, dangers to using any new drug - it takes a few years for the less common effects of a new drug to be noted - and it's important to remember that the side effect profile of this male pill was announced after 60 men took it for six months. That may be enough time to spot any obvious disasters and a reasonable size for preliminary research, but it's far too early to announce the pill a success.

So this is how the next five years will be spent - trying the drug on larger and larger numbers, watching for adverse effects, and fine tuning the ingredients to make the pill more palatable to men. But even when its safety has been proven, and it has been shown to reduce the sperm count to nil, will men actually take it?

With the psychosexual baggage that goes along with fertility, which all the safety data in the world could not carry away, it's hard to imagine anyone but the most new of new men taking this pill. A recent poll in Edinburgh found that two thirds of men questioned would take the pill if it was free from side effects. But do you seriously believe that?

It's quite revealing to look at what actually happens in the case of sterilisation. Despite vasectomies being safer, easier to perform, and 10 times less likely to result in accidental pregnancy than female sterilisation, every year more women have the snip than men.

Perhaps it's because vasectomies are not always reversible (and you never know when you might be called upon to repopulate the earth after global nuclear holocaust). But even if they're queueing round the block for the male pill, there's one other major hurdle, and it could be the killer. If many women can't trust themselves to remember to take their pill at the same time every day, will they trust men to do it? A woman has a fairly solid motive for remembering; men may have a fairly solid motive for keeping quiet when they forget.