Is there a male contraceptive?
How does the pill work? And why has it taken so long to get a male contraceptive?
Izzie Clarke received this question from listener Sophie. Reproductive physiologist Bill Colledge, from the University of Cambridge, started by explaining how the pill works...
Bill - The modern pill that females take actually prevents pregnancy in two ways. It contains two hormones usually. It's a synthetic oestrogen which is a female hormone and also a synthetic progesterone and they work in different ways. So the oestrogen component, what that does is it causes a thickening of mucus within the reproductive system and that makes it more difficult for the sperm to reach the egg. The progesterone part of it acts slightly differently, what that does is it suppresses the reproductive axIs and prevents ovulation, so there's this dual effect. You could get by just with oestrogen only, you don't have to have progesterone. But it's a bit like belt and braces, you've got both actions which will make the contraceptive much more effective.
But it's been a lot more difficult to make a male contraceptive. And the reason for this is just the way in which the body works and the difference between men and women. So if you think about women, they go through cycles and they produce an egg once throughout a 28 day period. Whereas men are making sperm continuously and it's much more easy to suppress one egg being released at one point in the cycle than it is to suppress the millions of sperm that are being made continuously by the men.
Izzie - So have we got to a stage that we can now have something similar that would work for men?
Bill - There's developments that are going on. Ideally what you want is an oral contraception for men, just like for the woman. The woman takes the pill and it gets into the body. Theoretically, you could give men analogues of testosterone and increase the testosterone levels which, eventually, would suppress sperm production. The problem with that is you can't take it orally. You ingest testosterone and most of it gets inactivated in the liver straight away, so you have to inject it which means that every week you have to have an injection of high level of testosterone and most people wouldn’t use that as a contraceptive. So that's how it would work but it's not possible to take it orally at this stage.
Izzie - And do you think there will be developments to get something like that or are we still not quite there yet?
Bill - There are developments aimed at having an oral contraception. One of the problems, of course, is that it has to be reversible. If someone stops taking it and then wants to conceive there's no point in having all of your germ cells dead in your testes, so it has to be reversible.