Everyday medicines make women ill as they have only been tested on men
Many pills most commonly used daily by women - such as painkillers and heart drugs - were never tested on females, pregnant or otherwise, before being put on the market, researchers have revealed.
This may explain who women are likelier to suffer side-effects from prescribed drugs than men, suggests some researchers.
"Women are about twice as likely to suffer side-effects from prescribed drugs as men," the Daily Mail quoted Dr Anita Holdcroft, a consultant anaesthetist at Imperial College London as saying.
Dr Holdcroft arrived at his figure by studying the latest official figures on reported side-effects, released earlier this year by the official drugs watchdog, the Medicines and Healthcare Products Regulatory Agency (MHRA).
Harmful side-effects are reported to the agency by doctors and patients.
Of course, men also react badly to drugs. But the fact that they report only half as many bad side-effects indicates women's problems differ widely in their scale and nature.
It may also be that women perceive side-effects differently than men - they may be more alert to their bodies' responses - but again, this has not been investigated properly.
Even with the most common drugs, such as non-steroidal anti-inflammatory painkillers, "we do not know how they affect women differently, even though these drugs are potentially dangerous," said Dr Holdcroft, who is a member of the Medical Women's Foundation, the largest organisation of women doctors in the UK.
There are no legal barriers to women participating in clinical trials, but practices in the pharmaceutical industry means they are often excluded.
This is particularly true when drugs are safety-tested in humans for the first time, with dosages gradually increased.
"Women are more variable as research subjects. They have hormonal cycles and child-bearing, and their responses to drugs may change again after the menopause," said Dr Holdcroft.
Drug researchers often avoid testing such variations because they complicate results, which is not what drug companies want.
As the first stage of clinical trials are aimed mainly at persuading regulators that a medicine is safe and effective enough to be licensed for profitable commercial use, drug company researchers focus on the more physically stable male sex.
Independent pharmaceutical consultant Dr Peter Dewland, who has been involved in running more than 100 human drug trials, said nearly all these studies have been on men - at the drug companies' request.
"Because the effect on fertility on drug trial results has not been adequately studied, we tend to use males. Even if we find a drug affects male and female animals differently in lab tests, we may not look hard for those problems when we test the drug on humans," he revealed.
"I was even asked to use men in a safety trial for a drug for helping women in labour. The pharmaceutical-industry client took some persuading to use women," he added.
However, Dr Dewland noted that proper trials of all drugs should involve women.
Women are generally smaller and weigh less than men, so may require different dosages or smaller pills, he said.
And women's bodies can absorb drugs differently and react to them in different ways, he added.