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Paracetamol can impair men’s ability to make women pregnant

New research has disconcerting news: Large quantities of paracetamol seem to affect the function of sperm cells and possibly men’s ability to make women pregnant.​

In a recently completed research study, researchers from Rigshospitalet and their French colleagues have investigated how paracetamol affects sperm cells in men. 

The new study reveals that the problem is not paracetamol in itself, but rather the type of metabolites paracetamol becomes in men's sperm. These metabolites interfere with the normal operation of the sperm cells, and thus possibly reduce men’s chances of making a woman pregnant.

The head of research at the Danish Headache Center at Rigshospitalet, David Møbjerg Kristensen, explains:

"This may explain the results of previous US studies, which have shown that men who have taken large quantities of paracetamol can find it difficult to make women pregnant. The possible link has caused concern, but we haven’t been able to explain why.” 

David Møbjerg Kristensen carried out the study with Dr. Anders Rehfeld from the Department of Growth and Reproduction at Rigshospitalet, and Anders elaborates: 

“The new study suggests that paracetamol is converted into metabolites that interfere with sperm cells’ ability to navigate to an egg. If the metabolites disturb this sense, sperm cells can find it difficult to find their way to the egg.”


​ Anders Rehfeld o​g David Møbjerg
The study includes examinations of three men who submitted semen samples, urine samples and blood samples in two phases. The first phase was at the beginning of the study, and the second was after five days, in which they were asked to take the maximum recommended dosage of paracetamol (4 x 2 tablets) every day. 

To the surprise of the researchers, the results showed that the paracetamol accumulated in the men’s semen. When they looked at the effect of paracetamol on sperm cells, the researchers found that the big problem is the metabolites that paracetamol is converted into by the sperm cells. 

Both researchers are concerned with the results. Both because the new findings could apply for other types of medication, and because once again there is evidence that paracetamol is perhaps not quite as harmless as many people think.

"It’s worrying that paracetamol appears to accumulate in sperm before it’s released. If this applies for a medicine like paracetamol, it is also likely to apply for other types of medication. Therefore, this is again a reminder that we must remember that paracetamol is a ‘proper’ medicine that may have adverse effects. 

Many people may perhaps have forgotten this, because they can buy paracetamol over the counter at a local store and therefore they don’t count it as a ‘proper’ medicine. In previous studies, we’ve seen that, if you ask ‘Have you taken medicine recently?’ most don’t mention paracetamol. This is worrying," explains David, who stresses that he recommends following the recommendations from the Danish Medicines Agency and taking as little as possible and for as little time as possible. And if you are in doubt, talk to your pharmacist or your general practitioner. ​​

The study has been published in Human Reproduction and it is the first of its kind to show a direct effect of Tylenol/acetaminophen/paracetamol on sperm cells in human beings. 

Previous studies from the National Institute of Health in the UK and others have demonstrated a correlation between adult males with high levels of acetaminophen/paracetamol in their urine and reduced semen quality, as well as problems making a woman pregnant, but none have been able to explain why. The new study could be the explanation, and therefore further investigation is required. 

On the basis of the new study, the researchers will initiate a larger study to confirm the new findings with more data. 

The study will be carried out by a Danish-French collaboration with Professor Arthur David from the French National Institute of Health and Medical Research (INSERM).


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