They may even see physical changes like decreases in body hair and muscle mass and development of breast tissue.
Researchers warned there was unlikely to be any nasty side effects from men who use the drug to combat their occasional headaches.
The men developed the condition just a third of the way through the study - with four weeks left to go of the 600mg dosage twice a day.
Levels of luteinising hormone, which stimulates testosterone production, increased as patients took the drug - but overall testosterone dropped.
The findings come amid male infertility concerns, particularly in western countries, where sperm counts have plummeted by 52 percent over the last 40 years.
The research team warned: ‘Ibuprofen appears to be the preferred pharmaceutical analgesic for long-term chronic pain and arthritis.‘Therefore, it is also of concern that men...