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i came accross a must read Q&A on t-mag by Cy wilson: -
Q: I hear a lot of people talking about femara on the Testosterone drug forum. What is it exactly and is it better than Arimidex?
A: Femara, or letrozole, belongs to the same class as anastrozole (Arimidex). They're both nonsteroidal aromatase inhibitors. Non-bootlegged letrozole is available as a 2.5 mg film-coated tablet in bottles of twenty. The half-life is about two days and absorption doesn't appear to be affected by food.
Even though 2.5 mgs per day is commonly used, 0.1 mg was shown to be just about as effective. Significant suppression of estradiol and estrone levels are typically seen within 24 hours of administration. (8, 9) As a side note, letrozole has been shown to cause a 38% reduction in plasma levels of tamoxifen when used concurrently, although I don't see why one would use the two together. (10)
Now, what about letrozole compared to anastrozole? Well, the following chart shows how various aromatase inhibitors did compared to one another (in vitro at least). (11)
Aminoglutethimide (Cytadren)… 1
Formestane… 60
Exemestane… 60
Anastrozole (Arimidex)… 200
Letrozole (Femara)… 200
Vorozole… 1000
Now, what does this mean? Well, in vitro, the two appear to be equivalent in potency. However, as you know, in vitro assessments aren't always accurate when compared to results that occur in vivo.
So, is there any in vivo evidence? Yes. Researches performed a double-blind crossover study using either 2.5 mg/day of letrozole or 1 mg/day of anastrozole. After six weeks of treatment for each substance it was found that when those patients used letrozole, there was a suppression greater than 99.1% (Estrone-84%, Estradiol-88%, estrone sulfate-98%) in all patients, whereas, anastrozole resulted in an average suppression of 97.3% (Estrone-81%, Estradiol-85%, Estrone sulfate-94%).
These differences were found to be significant after statistical analysis. (12) Now, I know some of you may construe this evidence as supporting the idea that anastrozole is indeed more potent since the mg amount used was less (2.5 mg vs. 1.0), and while this is true, you must recall that letrozole was found to have no statistically significant difference in estrogen levels amongst those who used 0.1-2.5 mg. This would indicate that 0.1 mg would also have outperformed 1 mg of anastrozole. (13)
One thing to note though is that there were adverse effects seen on blood lipids in patients using 2.5 mg/daily, more specifically, a reduction of HDL and an increase in LDL. Essentially, either make sure you use the drug as sporadically as you do androgens or use it along with clomiphene in order to keep blood lipids at a fair level. (14)
To be totally honest, either drug will do as they both suppress estrogen formation extremely well and to nearly similar levels, so much so that I doubt you'd actually notice the difference in terms of real world measures (i.e. chance of getting gyno, water retention, etc.) Still, if you want to argue which is technically more potent, it's letrozole (Femara).
BarPk
Q: I hear a lot of people talking about femara on the Testosterone drug forum. What is it exactly and is it better than Arimidex?
A: Femara, or letrozole, belongs to the same class as anastrozole (Arimidex). They're both nonsteroidal aromatase inhibitors. Non-bootlegged letrozole is available as a 2.5 mg film-coated tablet in bottles of twenty. The half-life is about two days and absorption doesn't appear to be affected by food.
Even though 2.5 mgs per day is commonly used, 0.1 mg was shown to be just about as effective. Significant suppression of estradiol and estrone levels are typically seen within 24 hours of administration. (8, 9) As a side note, letrozole has been shown to cause a 38% reduction in plasma levels of tamoxifen when used concurrently, although I don't see why one would use the two together. (10)
Now, what about letrozole compared to anastrozole? Well, the following chart shows how various aromatase inhibitors did compared to one another (in vitro at least). (11)
Aminoglutethimide (Cytadren)… 1
Formestane… 60
Exemestane… 60
Anastrozole (Arimidex)… 200
Letrozole (Femara)… 200
Vorozole… 1000
Now, what does this mean? Well, in vitro, the two appear to be equivalent in potency. However, as you know, in vitro assessments aren't always accurate when compared to results that occur in vivo.
So, is there any in vivo evidence? Yes. Researches performed a double-blind crossover study using either 2.5 mg/day of letrozole or 1 mg/day of anastrozole. After six weeks of treatment for each substance it was found that when those patients used letrozole, there was a suppression greater than 99.1% (Estrone-84%, Estradiol-88%, estrone sulfate-98%) in all patients, whereas, anastrozole resulted in an average suppression of 97.3% (Estrone-81%, Estradiol-85%, Estrone sulfate-94%).
These differences were found to be significant after statistical analysis. (12) Now, I know some of you may construe this evidence as supporting the idea that anastrozole is indeed more potent since the mg amount used was less (2.5 mg vs. 1.0), and while this is true, you must recall that letrozole was found to have no statistically significant difference in estrogen levels amongst those who used 0.1-2.5 mg. This would indicate that 0.1 mg would also have outperformed 1 mg of anastrozole. (13)
One thing to note though is that there were adverse effects seen on blood lipids in patients using 2.5 mg/daily, more specifically, a reduction of HDL and an increase in LDL. Essentially, either make sure you use the drug as sporadically as you do androgens or use it along with clomiphene in order to keep blood lipids at a fair level. (14)
To be totally honest, either drug will do as they both suppress estrogen formation extremely well and to nearly similar levels, so much so that I doubt you'd actually notice the difference in terms of real world measures (i.e. chance of getting gyno, water retention, etc.) Still, if you want to argue which is technically more potent, it's letrozole (Femara).
BarPk
