University of Edinburgh scientists found the painkiller interrupted the production of testosterone when given for seven days.
The hormone is key to the development of male reproductive organs.
NHS guidelines say paracetamol should be taken only if necessary in pregnancy and for the shortest possible time.
And anyone needing long-term treatment must seek medical advice.
The UK watchdog, the Medicines and Healthcare Products Regulatory Agency, says paracetamol is one of the few painkillers generally considered safe if expectant mothers absolutely need to take it.
It can also be important in treating fevers that could otherwise lead to harm
But previous studies have hinted that paracetamol could kick-start reproductive problems in the womb.