T Nation

Letrozole vs. Anastrozole


Seems I may have seen this somewhere on this forum, but I cannot locate it. Can anyone tell me what the difference between Letrozole and anastrozole? They are both AI (aromatase inhibitors) and they both seem to do the same job.

I was thinking that maybe Letrozole was the generic, but then that is what I also thought about anastrozole. I do know that Arimidex is a brand name.

So, can someone set the record straight? Also, is there any difference in effectiveness between them?


Anastrozole- comes in diffrent dosing such as .25mg tabs where as letro comes in 2.5mg tabs. The problem is you need to block some but not all estrogen because it is needed for growth. Letro may be more potent at blocking estrogen. The effectiveness depends highly on the person and which you react better to. Also letro can kill your sexdrive.


Thanks! I was looking at drops, not tablets and I was confused because they both appear to do the same thing. Was not aware of the tablet form. The larger dosage of letro would explain why it can kill sex drive.


Letrozole is the generic name for Femara. It is many more times more powerful than Arimidex (anastrozole) and is much more difficult to dose for TRT. It is capable of blocking something like 98% of estrogen conversion, which can cause problems if E2 is driven too low. It is not used much for TRT, and the reports of it's use are not very encouraging.

Even for bodybuilders on high dose aromatizing agents, the use of letro is not advised due to its unpredictable response and possibility of driving E2 into the ground. Its only reported benefit is the possible reversal of gyno in some cases.