US scientists have predicted the advent of a contraceptive drug without the side effects of the current generation of birth control pills. Speaking at the American Society for Reproductive Medicine's 63^rd annual conference, which finishes today, the scientists highlighted a technique known as "RNA interference", through which sperm is prevented from gaining access to the egg.

Among the side effects produced by oral contraceptives are headaches, nausea and a diminished sex drive, while they can also increase the chance of strokes and deep vein thrombosis. The new pill, however, will not be available for at least 10 years, and could come complete with its own set of side effects.

RNA interference is effectively a method by which a gene is silenced, and thereby ceases to function normally. The US researchers, who are based at Boston's Brigham and Women's Hospital, have discovered a gene which becomes active in eggs immediately prior to fertilisation. The gene, which is called ZP3, manufactures a protein which allows sperm to adhere to the outer layer of an egg. In the absence of this protein, fertilisation cannot take place.

The Boston researchers trialled the ZP3 gene in experiments involving mice, and found that, when it was silenced, pregnancy was an impossibility.

The team's research was described to the crowd at the conference by Dr Zev Williams, who stated: "We simply don't have a contraceptive drug that is non-hormonal and reversible".

He added: "What we are trying to do is to think about contraception in a new way. Obviously there are going to be hurdles and it is going to take a lot of time, but the need is there and we think it can be achieved."

In response to the presentation, the University of Sheffield's Professor Bill Ledger highlighted how side effects remained common in a large number of women taking the oral contraceptive. The US team's proposal, he said, represented "a new concept". He continued: "If it were available, I am sure a lot of people would want to take it. If it isn't hormonal, that's a big selling point."

As far as Cambridge University's Dr Martin Fabani is concerned, hurdles would need to be surpassed. Additionally, no guarantee could be made that the drug would be entirely free of side effects.

Said Dr Fabani: "RNA interference is fantastic and there was a big hype around it, but people are starting to see what we call 'off-target' effects - where the therapy has an unwanted effect elsewhere in the body.

He added: "Every single application has some degree of off target effects."

Source - Pharmaceutical International's US Correspondent

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