Now onto Femara (AKA Letrozole), which is more effective than Arimidex in it's ability to pass thru the cell membrane of lipid (fat) cells and inhibit the activity of aromatase -- Arimidex is just over 80% effective at inhibiting aromatase, Femara is around 95-97% Levels of estrogen are totally undetectable in any patients taking Letrozole
, and it has even been used to increase testosterone to normal levels (from sub-normal ones) and increase LH, FSH and SHBG (Epilepsy Behav. 2004 Apr;5(2):260-3). Other than that, both of these drugs stop the process of aromatization, rather than just blocking (competing for, if you prefer) the receptors as Clomid and Nolvadex do. An effective dose of Letrozole is 1-2.5 mg/day (I use 1mg/day), but be forewarned, it can kill your sex drive, and could decrease IGF levels.
On the other hand, I've seen studies where it increases IGF levels. Also worth noting is that there's a rebound effect when you come off Letrozol. What can I say? Letrozole's effects on serum lipids (cholesterol, both HDL and LDL) are, in the words of one researcher: "inconsistent.
"And compared with Aromasin and Arimidex, In non-cellular systems, letrozole is 2-5 times more potent than anastrozole and exemestane in its inhibition of the aromatase enzyme and activity, and in cellular systems it is 10-20x more potent! Letrozole (2.5mg daily) also achieved a much greater suppression of the plasma concentrations of both estrone and estrone sulphate (estrogens) than anastrozole (1mg daily) and a greater inhibition of in vivo aromatization also (sorry for the geek-speak.it's over for now.). ( J Steroid Biochem Mol Biol. 2003 Oct;87(1):35-45.) Exemestane can also cause androgenic sides (Clin Cancer Res. 2003 Jan;9(1 Pt 2):468S-72S.)(1. J Clin Endocrinol Metab 2000 Jul;85(7):2370-7 2. J Steroid Biochem Mol Biol 1997 Nov-Dec;63(4-6):261-7). I've used Letrozole, and it cleared up my minor gyno lumps, to the point that they are totally gone now.
Lets talk about Arimadex (Anastrozole), now. From the research I've done, this seems to be one of the best ancillaries around
and I'll tell you why. First off, 'dex is an aromatase inhibitor (AI.remember what that is?). 1mg per day of this stuff (J Clin Endocrinol Metab 2000 Jul;85(7):2370-7, "Estrogen Suppression in Males") was shown to decrease estrogen by 50% and increase testosterone levels by 58%. LH and FSH also went up slightly.
The test increase didn't happen at a dose of .5 per day, but estrogen suppression was the same. Anastrozole also raises IGF1 and shows a trend towards increasing IGF2
(J Steroid Biochem Mol Biol. 2002 Apr;80(4-5):411- BTW, literature provided by the original maker of Arimadex states that stable blood plasma concentrations of the compound are achieved after 7 consecutive 1mg daily doses. All of that plus the usual blood lipid changes we've seen with most of the anciliaries we've looked at! Anyway, that's a pretty hefty decrease in estrogen, even at .5mg/day.
For my money, if I wanna stop aromatization during a cycle, I'm gonna use Arimadex at .5mgs per day or Letrozole at 1mg/day. They are perfect during-cycle ancillaries. Unfortunately, you need to take Anastrozole for a week to get a steady level of it in your blood
(same thing goes for Exemestane), wheras you need to take Letrozole for 60 days to get a steady blood plasma level.
Though Anastrozole has a ½ life of 41-48 hours, and exemestane has a ½ life of 27 hours, Letrozole has a whopping 2-4 day (!) ½ life (Clin Cancer Res. 2003 Jan;9(1 Pt 2):468S-72S.).