Why you might not be buying the right pain relief for period cramps
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Many women may not be using the most effective pain medication for period cramps, according to a big study of supermarket till receipts.
A decade of loyalty card data across 211 million transactions in an unnamed chain of high street stores in England found paracetamol was the most common painkiller bought alongside tampons and sanitary towels.
But experts say ibuprofen could be a better choice for many because it is more effective at dealing with muscle cramps.
The transactions reveal the "scale and impact" of period pain and how people manage it, which has not been studied much before, say the researchers.
Paracetamol is perhaps more familiar to people which might explain why it was bought more often, they suggest.
While still an effective painkiller, ibuprofen can be a better choice for period pain because it blocks the production of prostaglandins - the chemical responsible for causing the cramping contractions of muscles in the womb.
Paracetamol, meanwhile, works primarily in the brain to block pain signals, making it a good choice for headaches. It also helps manage a high temperature, so can be useful if you have flu, for example.
Researchers looked at purchases from 3.4 million shoppers between 2006 and 2015.
Half of menstrual product transactions also included a pain product, the study published in PLoS Digital Health journal found.
Of those pills, around two-thirds were paracetamol-based and the other third being ibuprofen.
Co-researcher Dr Anya Skatova, from Bristol University, stressed that the data is more of a snapshot rather than fully representative for the nation. But it does provide some hints about what women are buying as period pain relief.
Most often, cramping is a normal part of the menstrual cycle when the womb muscle contracts to help shed its lining as a period.
During this time the body makes hormone-like substances, called prostaglandins, but higher levels have been linked with more-severe menstrual cramps.
Investigator Prof James Goulding, from Nottingham University, said there was a real public health education opportunity here and highlighted the lack of research into period pain relief.
"I don't think I'm going out on a limb here by saying that if men got period pain, we'd know a lot more about it by now," he told BBC News.
Ibuprofen is a non-steroidal anti-inflammatory drug that reduces swelling as well as easing pain, plus it lowers prostaglandins. Paracetamol does not have these anti-inflammatory properties.
It is best to start taking ibuprofen the day before, or several days before, a period or pain is expected - before the body produces prostaglandins - says the charity Endometriosis UK.
If you experience severe period pain that stops you from doing day-to-day things, or that worries you at all, you should speak to your doctor, says the NHS.
Like any medication, pain relief tablets can cause side effects. Ibuprofen is not suitable for everyone. Check the product information inside packs before taking any.