Drugs regularly taken to alleviate back pain 'significantly' reduce a woman’s fertility, doctors have warned.

Researchers found a group of drugs, known as non-steroidal anti-inflammatory drugs (NSAIDs), ‘significantly inhibit ovulation’.

NSAIDs are among the most commonly used drugs worldwide, and are taken by more than 30 million people every day.

Available without prescription, they are largely used for the treatment of pain, inflammation and fever - all common features of conditions involving joint and muscle pain.

They include naproxen, diclofenac, ibuprofen and aspirin. 

The researchers analysed the effects of three NSAIDs, diclofenac, naproxen and etoricoxib, on fertility.

When taking the drugs, only six to 27 per cent of women ovulated, depending on the type of drug they took. 

Doctors said the risk of reduced fertility associated with the drugs, must be communicated to women regularly taking the medication.  

And they suggest the drugs could also be researched as a potential contraceptive.

'After just ten days of treatment we saw a significant decrease in progesterone, a hormone essential for ovulation, across all treatment groups, as well as functional cysts in one third of patients,' said study investigator, Professor Sami Salman, of the University of Baghdad, Iraq.

'These findings show that even short-term use of these popular, over-the-counter drugs could have a significant impact on a women's ability to have children.

‘This needs to be better communicated to patients with rheumatic diseases, who may take these drugs on a regular basis with little awareness of the impact.'

As part of the study, Professor Salman and his team tested three of the most commonly prescribed NSAIDs: diclofenac, naproxen and etoricoxib.

They recruited 39 women of childbearing age who suffer from back pain to take part in the study.

The women received diclofenac (100mg once daily), naproxen (500mg twice daily) and etoricoxib (90mg once daily) or a placebo.

The drugs were given 10 days after the beginning of their menstrual cycle - the first day of a woman’s period.

Researchers tested whether the women had ovulated by analysing the level of the hormone progesterone, via a blood sample.

They also measured the diameter of the dominant follicle, a fluid-filled cavity in the ovaries that contains one undeveloped egg, using ultra sonography – a form of ultrasound.

Rupturing of the dominant follicle, and subsequent release of an oocyte - an unfertilised egg - is essential for ovulation to occur.

Of the women receiving NSAIDs, only 6.3 per cent of those taking diclofenac ovulated, they found.

And only 25 per cent of women taking naproxen and 27.3 per cent taking etoricoxib ovulated.

This was compared with 100 per cent of women in the control group, who were not taking medication.

Professor Salman concluded: 'These findings highlight the harmful effects NSAIDs may have on fertility, and could open the door for research into a new emergency contraception with a more favourable safety profile than those currently in use.’