The male menopause does exist - but it is rare, researchers have concluded.
Just days after it was dismissed as a myth, the European team said the male menopause did exist - but that it affects only 2% of middle-aged men.
Over 3,300 men from across Europe were assessed for the New England of Journal study.
A men's health expert said testosterone therapy could be beneficial, but doctors had to be cautious about its use.
Scientists led by a team from the University of Manchester looked at the testosterone levels of 3,369 men aged 40 to 79 from eight European centres.
The men were also asked about their sexual, physical and mental health.
Three sexual symptoms - poor morning erection, low levels of sexual desire and erectile dysfunction were linked to low testosterone levels.
Depression, fatigue and an inability to perform sexual activity were also linked.
But some symptoms commonly cited as being indications men are going through a "menopause" including changes in sleeping patterns, poor concentration, feeling worthless, and anxiety were found to have no link to low testosterone levels.
The condition, also called late-onset hypogonadism, was also found to be linked to poor health and obesity.
Hypogonadism is a condition where the testes fail to work properly, affecting hormone levels.
'Excessive diagnosis' warning
Professor Fred Wu, from the University of Manchester's school of biomedicine, who led the study, said unlike classical hypogonadism where similar symptoms were accompanied by an diagnosable condition, that was not the case for late-onset hypogonadism.
"This well-practised diagnostic approach is frequently found wanting when dealing with the age-related decline of testosterone in elderly men who are prone to have a significant background of non-hormone-related complaints."
He added: "Our findings have for the first time identified the key symptoms of late-onset hypogonadism and suggest that testosterone treatment may only be useful in a relatively small number of cases."
Professor Wu said sexual symptoms were relatively common even in men with normal testosterone levels.
"It is therefore important to specify the presence of all three sexual symptoms of the nine testosterone-related symptoms we identified, together with low testosterone, in order to increase the probability of correctly diagnosing late-onset hypogonadism.
"The application of these new criteria should guard against the excessive diagnosis of hypogonadism and curb the unwise use of testosterone therapy in older men."
Earlier this month, an editorial in Drug and Therapeutics Bulletin said many men who report symptoms have normal hormone levels and warned giving synthetic testosterone as it could increase the risk of prostate cancer.
Dr Ian Banks, president of the Men's Health Forum, said: "We need to be very cautious about the prescribing of testosterone therapy, and doctors need to balance the benefits against the risks.
"This research acknowledges it's a complex issue, and that caution is needed."