WOMEN who use oral contraceptives could suffer a long-term loss of sex drive after coming off the pill, according to new research.

American scientists have discovered that a chemical produced by the pill to stop ovulation continues to suppress testosterone levels — central to desire in men and women — for up to a year after women stop taking it.

A seven-year study shows that women on the pill had four times the level of sex hormone binding globulin (SHBG), which stops testosterone from circulating in the body, as those who had never taken the pill.

Yet even 12 months after they stopped using the pill, women had twice as much of the chemical in their bodies as those who had never used oral contraception.

The findings will be of concern to the 100m women around the world, including 3.5m in Britain, who use oral contraceptives.

Loss of libido, muted or non-existent orgasms and painful intercourse have long been known as side effects of the pill. But previous research has suggested a woman’s sex drive can return to normal within four weeks of discontinuation.

Dr Claudia Panzer, an endocrinologist in Denver, Colorado, and lead author of the new study, said: “It is important for physicians prescribing oral contraceptives to point out to patients the potential sexual side effects.”

Panzer’s research, published this month in the Journal of Sexual Medicine, was based on 124 pre-menopausal women attending a clinic for sexual dysfunctions.

Half the women had used the pill, 39 had stopped using it and 23 had never taken it. Scientists measured their SHBG levels every three months for a year.

A spokeswoman for the UK Family Planning Association urged caution in interpreting the findings. “It is difficult to quantify what a person’s sex drive is,” she said.

“It may be influenced by a range of lifestyle factors. Whether you are stressed, what you have eaten or how much you have drunk can all affect your sex drive. Whether you have children and what ages they are can also have an effect. Our problem is that none of these factors was quantified in this research.”

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