Pregnant women should be very careful when taking paracetamol because long-term use of the medicine could adversely affect the reproductive health of their sons, a newly published study warned.

Scientists at the University of Edinburgh have found that the painkiller interrupted the production of testosterone when given for a week. This hormone plays a key role in the development of male reproductive organs.

According to NHS guidelines, one should take paracetamol only if necessary in pregnancy and that too for the shortest possible time. In case anyone requires long-term treatment, seeking medical advice would be in the best interest.

The Medicines and Healthcare Products Regulatory Agency, the UK watchdog, said that paracetamol is among those few painkillers that are generally considered safe if expectant mothers absolutely need to take it.

Earlier, studies have indicated that paracetamol could kickstart reproductive problems in the womb.

For instance, a Danish research has found women who took painkillers were more likely to give birth to boys with un-descended testes. Such a thing could sometimes lead to future reproductive troubles.

In order to determine the reason behind this link, the scientists have engineered a system to mimic the conditions of human pregnancy as closely as possible.

Researchers implanted the mice with human foetal tissue and gave them paracetamol for a week. They had very low levels of testosterone in their blood as compared to those given a dummy drug. But there appeared to be no effect when given doses for just one day.

The lead researcher Dr. Rod Mitchell, said, "This study adds to existing evidence that prolonged use of paracetamol in pregnancy may increase risk of reproductive disorders in male babies".

He advised that pregnant women should follow current guidance, saying that painkiller should be taken at the lowest effective dose for the shortest possible time.

In addition the researchers have cautioned that at present it's too early to tell that to what extent their findings apply to humans. They have pointed out that a study on pregnant women could not be carried out for ethical reasons.