Doctors cautioned that taking birth control pills could wreck a woman’s sex life.

Women may benefit from the freedom to make love as much as they like without fear of getting pregnant after taking contraceptive pills but it could also switch off their desire.

The pill has been linked with many side effects including blood clots, migraines and weight gain but perhaps the least discussed is its propensity to dampen libido by decreasing testosterone levels.

Contraceptive drugs curb the hormone’s production in the ovaries and also increase levels of sex hormone binding globulin (SHBG) – a substance that effectively takes it out of play because testosterone-bound SHBG is considered biologically inactive.

But it is uncertain how regular problems are in pill users and until now any sexual dysfunction – including loss of libido, subdued or non-existent orgasms or painful intercourse – was believed to be reversible when women stopped taking the drug.

Boston University’s Dr Irwin Goldstein and colleagues studied 125 young women who attended a sexual dysfunction clinic. Sixty-two of them were taking oral contraceptives, 40 had previously taken them and 23 had never taken them, reports New Scientist.

The team measured levels of SHBG in the women every three months for a year and found in pill users they were seven times as high as in women who had never taken them.

Levels fell in women who had stopped taking the oral contraceptive – but remained three to four times as high as in those who had never taken it, the researchers told a meeting of the American Association of Clinical Endocrinologists in Washington DC last week.

Dr Goldstein said: “There’s the possibility it’s imprinting a woman for the rest of her life.”

He says the most common problem for women is lack of libido – or sexual desire – which he believes is a result of sex steroid hormone levels gone haywire.

He said: “Women who are on the birth control pill have huge problems with sex steroid hormone levels.”

But Dr Goldstein believes there’s room for drugs in sex therapy. He says those who reject the medical approach to women’s sexual troubles aren’t seeing the bigger picture.

He said: “It took us 20 years to understand the physiology of men’s erections. We have to do the basics before we can get to the therapeutics that have efficacy.”