Two new studies have shed light on the impacts of two of the most common painkillers.

In one report, researchers found that ibuprofen could alter the hormonal system of men, impacting important aspects of testicular function, including testosterone production.

In another, it was found that taking paracetamol during pregnancy may impair the future fertility of female offspring.

A paper from the University of Copenhagen published in PNAS  reports on a series of studies investigating the impact of the common analgesic ibuprofen on testicular function.

This class of medication has long been known to cause gastrointestinal upset and aggravate asthma, its link with impaired male hormonal function is not well established.

The investigators found that when healthy young men took a moderate dose of ibuprofen, equivalent to three tablets of Nurofen per day, for six weeks, it impaired the function of two testicular cell types responsible for the production of testosterone and supporting sperm development.

The investigators also report that ibuprofen added to testicular cells in culture was capable of blocking the action of key enzymes involved in the production of testosterone.

The findings support the possibility that anti-inflammatory drugs like ibuprofen could result in lower testosterone levels if taken over several weeks.

“Sperm quality was not assessed in the study, but as testosterone and Sertoli cell function play a key role in sperm production there is some theoretical concern that long term use of this drug could potentially negatively impact on male fertility potential,” said Professor Kelton Tremellen, a gynaecologist and Professor of Reproductive Medicine at Flinders University.

“However, it is presently uncertain if taking a couple of ibuprofen tablets with a headache would cause any significant impairment of testicular function. I believe it is highly unlikely to be the case.”

Dr Tremellen advised that men should be cautious and not take anti-inflammatory medication for long periods of time without consulting their doctor, especially if they were experiencing symptoms of low testosterone (fatigue, poor libido and mood) or infertility.

The paracetamol paper – presented at the Endocrine Connections conference and published in Bioscientifica - reviewed existing studies and concluded that giving mice and rats paracetamol during pregnancy may impair the future fertility of their female offspring. 

The researchers looked at the results of three separate studies which all reported altered development in the reproductive systems of female offspring when the mother rodents were given paracetamol during pregnancy. 

Lead researcher Dr David Kristensen and colleagues from Copenhagen University Hospital found that rodents given paracetamol during pregnancy, at doses equivalent to those that a pregnant woman may take for pain relief, produced female offspring with fewer eggs.

This means that in adulthood, they have fewer eggs available for fertilisation, which may reduce their chances of successful reproduction, particularly as they get older.

“Although this may not be a severe impairment to fertility, it is still of real concern since data from three different labs all independently found that paracetamol may disrupt female reproductive development in this way, which indicates further investigation is needed to establish how this affects human fertility,” Dr Kristensen said.

Although there are parallels between rodent and human reproductive development, these findings have yet to be firmly established in humans. However, establishing a link between paracetamol taken by mothers during pregnancy and fertility problems much later in the adult life of the child will be difficult.

Dr Kristensen recommends that an inter-disciplinary approach be taken to address this; “by combining epidemiological data from human studies with more experimental research on models, such as rodents, it may be possible to firmly establish this link and determine how it happens, so that pregnant women in pain can be successfully treated, without risk to their unborn children.”

“As scientists, we are not in the position to make any medical recommendations and we would urge pregnant women in pain to consult with their general practitioner, midwife or pharmacist for professional advice,” he said.