"We are now demonstrating the sexual and hormonal effect of two popular oral treatments for ED," Dr. Emmanuele A. Jannini from University of L'Aquila told Reuters Health. "Both were efficacious and able to increase testosterone levels after 3 months of treatment."

Jannini team studied 74 men with erectile dysfunction and found that free and total testosterone levels rose, overall, by about 50% after treatment.

The testosterone increases were more marked in the group that took Cialis than in the Viagra group, although the drugs were equally effective in restoring sexual potency, the investigators report in the medical journal.

The frequency of full sexual intercourse was also higher with Cialis (known chemically as tadalafil), despite the use of identical numbers of pills per month, the researchers note, "strongly suggesting that the greater normalization of hormonal values in tadalafil-treated patients was due to the higher number of sexual acts."

The higher frequency of sex "can be considered as an important benefit of tadalafil and a cost-effective advantage" for couples, the investigators suggest.

"For a man in a stable couple relationship, tadalafil is to be preferred," Jannini commented.

In this setting, the drug can be taken twice a week to allow spontaneous sexual activity. "From a psycho-sexological point of view, this may help the patient to considered himself 'cured' and not simply 'treated' for the symptom," he concluded.