Thirty-one men were given the maximum limit of 600 milligrams (or three tablets) of the drug each day for six weeks, a dosage commonly used by athletes. Other study participants were administered a placebo.
In just two weeks, the researchers found the men who took ibuprofen had an increase of luteinizing hormones, which males use to regulate testosterone production. This hormonal condition typically begins (if it ever does), during middle age.
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At the same time, the ratio of testosterone to luteinizing hormones decreased — a sign of dysfunctional testicles.
"The increase indicated that the drug was causing problems in certain cells in the testicles, preventing them from producing testosterone, which is, of course, needed to produce sperm cells," Medical XPress reported.
As a result, the body’s pituitary gland responded by producing more of a different hormone, essentially compensating for ibuprofen’s effect on testosterone production. This phenomenon is called compensated hypoganadism, which can reduce sperm cell production and infertility, the scientists wrote. The condition is also associated with depression and increased risk for heart attack and stroke.
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Because the small group of young male participants who took the drug only consumed it for a short time, "it is sure that these effects are reversible," Bernard Jégou, co-author and director of the Institute of Research in Environmental and Occupational Health in France, told CNN. Compensated hypoganadism can lead to a temporary reduction in sperm cell production, but that's not cause for alarm.
The larger concern, Jégou noted, is that using the drug for much longer periods of time could lead to a much more serious issue: overt primary hypoganadism, "in which the symptoms become worse — sufferers report a reduction in libido, muscle mass and changes in mood."
The medical community, including study authors, believe larger clinical trials are needed to understand ibuprofen’s effects men using low doses of the drug and whether or not long-term effects are indeed reversible.
Read the full study, recently published in the journal "Proceedings of the National Academy of Sciences of the United States of America."