Irritable male syndrome is a newly-recognized medical condition that turns confident, aggressive males into withdrawn, grumpy wimps. It?s caused by a sudden drop in testosterone, and affects men as well as animals, according to Gerald Lincoln of the Medical Research Council?s Human Reproductive Sciences Unit in Scotland.

The symptoms may resemble those of male menopause, but Lincoln believes the condition can affect men of any age when stress causes testosterone levels to suddenly fall.

Lincoln first noticed the syndrome in Soay sheep. In the autumn, during the mating season, the rams? testosterone levels soar. In the winter, testosterone levels fall and they lose interest in sex. High testosterone is supposed to mean more aggression, but the rams were more likely to injure themselves when their testosterone was low.

Lincoln monitored the activity of eight rams, including how often they butted other rams with their horns. As their testosterone levels fell, the rams changed from competent males to nervous, withdrawn animals. Red deer, reindeer, and Indian elephants also show clear signs of irritable male syndrome when testosterone levels fall off at the end of their breeding seasons, says Lincoln.

The male brain is loaded with receptors for testosterone. Richard Anderson, a colleague of Lincoln?s, found that when men who cannot produce testosterone go off hormone replacement therapy, they become irritable and depressed. Their mood improves when they resume treatment.

Lincoln thinks that stresses such as bereavement, divorce or life-threatening illnesses can send testosterone levels down. There are few human studies on stress and testosterone, but many studies on animals, including primates, showing that testosterone levels fall when stress sends corticosteroid levels higher.

?It?s right on the money,? says reproductive endocrinologist David Abbott of the Wisconsin Regional Primate Research Center. ?Testosterone effects have been missed. When a bloke gets grumpy and irritable, [researchers] try and explain it only in terms of cortisol levels and depression. They ignore the fact that testosterone levels are probably falling too.?

But David Handelsman, an expert on male hormones at the University of Sydney in Australia, says the changes in testosterone levels in normal adult men are far smaller than the dramatic swings seen in Soay rams.

If irritable male syndrome does affect men, it won?t be easy to diagnose. Doctors don?t know what normal human testosterone levels are and worry that extra doses of the hormone may increase the risk of heart disease. But it may be worth investigating.

Abbott says, ?Instead of putting stressed men on Prozac, a little testosterone may do the job.?

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