If he took it only once, probably nothing would happen, except perhaps side effects such as nausea. As for regular, long-term use, the effects would depend on the type of the pill taken: combined or progestogen-only.The combined pill contains oestrogens, which are responsible for the development of female secondary sexual characteristics, so a combined pill would cause slow changes in some body features that would vary from man to man.The first changes would probably be visible within two to three months. The man's breasts would start to grow, with his nipples becoming larger. His skin would become thinner and softer, which would lead to change in skin tone - pink, with the veins more visible. Body fat would start accumulating in "female areas", such as under facial skin - making his face look puffier - and also around his hips, thighs, upper arms and pubis.More significant changes, such as a slimmer waist-to-hips ratio and fleshier hips and buttocks, would probably take many more months to develop. His muscles might become thinner, and his body and scalp hair might change in texture, but the pill alone would not inhibit the growth of facial hair or improve male pattern baldness. Sweat production would also change, as would the body odours of skin, sweat and urine, which would become less sharp and more sweet and musky.The pill-taker would notice some emotional changes too, such as a greater tendency towards mood swings or depression. Recent studies have indicated that cross-hormone therapy in male-to-female transsexual people may result in a reduction in the volume of the brain towards female proportions - but with no effect on IQ. Regular intake of oestrogens would also increase the risk of blood clotting, decrease insulin sensitivity and cause disturbances in liver function.By contrast, the hormones in the progestogen-only pill do not cause feminisation in a male. Some studies show that they act like anti-androgens and would probably suppress testosterone to some degree, causing breast growth and a decrease in facial hair. This pill might raise the taker's body temperature and cause fluid retention.I could not find any clinical studies, but it seems certain that some will have been done, because oral contraceptives have been widely used in gender reassignment for men who want to become women.Joanna Jastrzebska, North Shields, Tyne and Wear, UK

I was a guinea pig for a trial a few years back which involved exactly this, as part of research into a male contraceptive pill. The trial lasted one week, during which some of us were given a common oral contraceptive but at four times the dose prescribed to women, while others were given the same quantity of the same hormones by injection. I was in the second group.The first day I didn't notice much difference, so I assume a man taking a single pill would be unaffected. The second day, I felt a little down and emotional. My libido started to diminish. On the third day, I was tearful.I don't know what happened to my testosterone levels, but I wasn't interested in going to the gym any more. More than usual, I wanted to eat chocolate and chat to my female friends. Yes, I am being serious. Little things like events in a movie would start me crying. This stabilised at around the fourth day. On the seventh day I took the last dose of hormone and the effects wore off within a couple more days. The doctor in charge assured me there would be no lasting changes.All in all, I feel I've had an insight into what it feels like to be a woman. I suspect that it would certainly work as a contraceptive (beyond its chemical effect) because I had no interest in sex, but I doubt many men would want to take female hormones at the expense of their "manliness". It was an interesting experience, but not one I wish to repeat.R. Ross, Aberdeen, UK

What, I assume, they are referring to is a contraceptive (birth control) pill that would work to block sperm production. I have read scientists are working on this but I think there may be a problem with the "male species" taking the birth control pill every 24 hours as recommended to prevent pregnancy.The "female species" have more of an incentive to take the birth control pill on time due to the fact they would become pregnant if they did not take the pill. Males would not have that incentive and may be lax in taking it every 24 hours---every day---365 days per year, and so on. I think we would have a lot of angry females, in addition to a big population explosion!