Most female employees have suffered period pain so strong it affects their ability to work, says a survey for the BBC.
The YouGov study of 1,000 women found 52 per cent had been hit, with nearly a third of those taking at least a day's sick leave as a result. However, just 27 per cent had told their employer that period pain was responsible.
Almost all the women surveyed - nine out of ten - reported having suffered from period pain at some point.
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The results have led one doctor to suggest employers should offer "menstrual leave" - and women be more open about discussing the issue.
"Menstruation is normal, but some women suffer terribly and they suffer in silence," said consultant gynaecologist Dr Gedis Grudzinskas.
"I don't think women should be shy about it and companies should be accommodating with leave for women who are struggling with painful periods."
Employment lawyer Fiona Morrison said severe period pain could be considered a disability.
"Under UK law, if someone is in extreme pain and it is stopping them from working effectively, a tribunal could say that this woman is disabled," she said.
One of the women surveyed, Nancy Eccles, left full-time work partly because of her painful periods. "I always soldiered on at work but in my last two years of teaching full-time, I struggled to get through an hour's lesson," she said.
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