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Letrozole, the new anti-estrogenic T booster

Men who take 2.5 mg letrozole daily will notice that their testosterone levels double and the concentration of estradiol in their blood decreases by 45 percent. Urologists at the University of Mersin in Turkey write about this soon in Fertility & Sterility.



Letrozole [structural formula shown here] is the active ingredient in Novartis’ Femara. Letrozole inhibits the enzyme aromatase [structural formula also shown here], which converts testosterone analogues into estradiol.

In men with relatively high amounts of estradiol and low amounts of testosterone in their blood, the testes theoretically work less hard. So the researchers did an experiment with 27 infertile men. The subjects were given a pill every day for six months that contained 2.5 mg letrozole. More than half of the subjects produced virtually no sperm cells.

The table below shows that the treatment increased the subjects’ testosterone level and lowered their estradiol level. Both quantity and quality of sperm cells increased.

No serious side effects were observed either. A few men developed mild headaches, but these were not serious enough for them to withdraw from the trial.

In a Dutch study with overweight men, the subjects’ testosterone level quadrupled when they took a weekly pill containing 2.5 mg letrozole. In a Canadian case study, a daily 2.5 mg dose doubled the subjects’ testosterone levels. [Fertil Steril. 2009 Aug;92(2):829.e1-2.]

Although all the studies mentioned here used men who had some kind of problem, we at Ergo-log, unhindered by scientific insight, dare to make the following pronouncement: athletes who want to increase their testosterone production are better off taking letrozole once every 5-7 days rather than daily.

Fertil Steril. 2010 Oct 8. [Epub ahead of print].

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