Letrozole

Letrozole is Novartis’ entry into the breast cancer treatment world. It’s a Type-II Aromatase Inhibitor (AI), which means that it competitively binds to the aromatase enzyme and inhibits the enzyme’s ability to metabolize testosterone into estrogen. This drug was developed to fight breast cancer by inhibiting the aromatization.

Letrozole is probably the most powerful Aromatase Inhibitor used by athletes today. It has been shown to reduce estrogen levels in women with breast cancer by 98% or more [1]. SO clearly, it’s useful for administration to male steroid using athletes who are eager to prevent some of estrogen’s nastier effects on their bodies- development of breast tissue, water retention, etc…

When we take a look at its effects in men, Letrozole actually reduced estrogen in one test subject to undetectable levels ^[2]. In another clinical study, intravenous administration of Letrozole (2.5mcg for 28 days), Letrozole lowered Estrogen by 46% in the young men tested, and 62% in the elderly subjects. In addition, Letrozole also significantly increased LH levels to a whopping 339 and 323% in the young and the elderly, respectively and Testosterone by 146 and 99%, respectively. [3] Letrozole was also able to produce a peak LH response to Gonadatropin Releasing Hormone equal to a 152 and 52% increase from baseline in either young or older men, respectively.

As you can see, Letrozole is a very powerful drug, and as a result, only very tiny doses are necessary. An effective daily dose of Letrozole for most people is usually about .25-.5mg/day, even though clinically, it is typically used at 2.5mgs/day. Twenty micrograms of Letro was enough, in one study done on men, to reduce estrogen levels by almost a third. [4]

Letrozole’s effects on cholesterol are, really difficult to pin down precisely. They are, in the words of one researcher: "inconsistent.” I can tell you that in my opinion, reducing your bodies estrogen to virtually nothing, will eventually take its toll on your cholesterol profile, and will kill your sex drive and your joints- all of which require estrogen to function safely and effectively.

Even if you take very low doses of Letrozole, it will build up to reasonable blood plasma levels, as it has a 2-4 day half-life, and this long half life also means you need to take Letrozole for 60 days to get a steady blood plasma level [5], and that it will take a very long time to clear out of your system.

Letrozole is the only pharmacological “cure” for gyno that I know of to have ever worked in bodybuilders. In a study conducted on rodents, Letrozole was able to effectively destroy breast tissue tumors [6], and it’s also been effective on many bodybuilders who have used it to eliminate an existing case of gynocomastia. In my case, I used Letro to get rid of my own gyno, by starting with a dose of 2.5mgs/day and then lowering it by .25mcgs per week once my symptoms abated.

With regards to using this stuff on a cycle, unless you are extremely gyno prone, or need to reduce estrogen levels to virtually nothing (for a bodybuilding contest or whatever), it’s going to be too powerful for most people. Male and female competitors typically use it to get the last bits of estrogen related water retention out of them during the final weeks of contest preparation. But when used on a typical cycle, Letro is generally overkill unless a ripped look with zero water and estrogen is desired or if the user is prone to gyno.