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12.07.2009

Some erection drugs have anti-oestrogenic effect

Erection drugs like Viagra/sildenafil or Cialis/tadalafil inhibit the enzyme PDE5, thus making erections easier. Andrologists at the University of Rome 'La Sapienza' discovered that tadalafil at least also inhibits aromatase, the enzyme that converts testosterone into estradiol.

Tadalafil remains effective for a day and a half after being taken, whereas sildenafil is only active for half a day. It was already known that men who take sildenafil or tadalafil produce a little more testosterone. Italian researchers published a study on this in 2004 in Clinical Endocrinology. [Clin Endocrinol (Oxf). 2004 Sep;61(3):382-6.]

The article describes their study of seventy impotent men, who took 50 mg of Viagra or 20 mg of Cialis for three months. The men's hormone levels were normal, although their free testosterone was on the low side. The men took five pills a month. The medicine worked and their sex life returned to normal. After three months their blood concentrations of total testosterone and free testosterone were a little higher. Their LH concentration had gone down.

The men had sex five to seven times a month on average. The sex was probably what caused the rise in testosterone level, the researchers suspect. According to the literature, sexual excitement increases the testosterone level, the researchers claim. That erection drugs have hormonal effects they say is unlikely.

Their colleagues, who published their research two years later, are of a different opinion. They examined twenty men who had been using Cialis for a year. The men took 10 mg doses, but were allowed to go up to 20 mg. The men took a pill on average ten times a month, and had sex eight times a month. When the researchers examined the men’s blood, they noticed that the testosterone concentration had increased by a tiny amount [the effect was not significant] and the estradiol concentration had gone down.

The effect on the estradiol was statistically significant. It only occurred, however, in the men that did not have too much body fat. The researchers found no effect on the estradiol level in the men with a BMI of 27 or higher. These men probably have aromatase in their fat reserves, which takes no notice of tadalafil and happily continues to convert testosterone into estradiol.

The researchers are cautiously optimistic about their discovery. "Any presumable effect of PDE5 on aromatase activity should be further confirmed with both in vitro and in vivo studies because it may open a new research avenue, for example, atherosclerosis, prostate disease, breast cancer, and osteoporosis", they write in their concluding paragraph.

Source:
J Sex Med. 2006 Jul;3(4):716-22.