Arimidex Side Effects
Throughout this profile, it is clearly stated that the use of Arimidex (or any aromatase inhibitor) should be for the purpose of controlling estrogen, not eliminating it.
The reduction of estrogen in the body can cause negative changes and problems in the body, especially if estrogen is suppressed for a long period of time using an aromatase inhibitor.
Arimidex side effects are generally manageable and mostly manifest very differently in men than in women using Arimidex, as it has been previously demonstrated in this profile that it affects women more than men due to their different endocrine physiology.
Side effects related to decreased estrogen
Almost all Arimidex side effects are the result of a decrease in total circulating estrogen levels in the body due to the inhibition of the aromatase enzyme.
The following are the main potential Arimidex side effects associated with decreased estrogen.
Joint and bone pain
An increased incidence of fractures has been demonstrated with Arimidex use in postmenopausal women with breast cancer [1].
However, this has been found to be mostly due to the fact that women are more sensitive to the decreased estrogen levels of Arimidex, and is generally a result of long-term use of Arimidex.
In fact, estrogen is an important hormone for promoting and maintaining bone mineral content, which promotes bone strengthening.
That's why postmenopausal women are more likely to develop osteoporosis as their estrogen levels naturally decline with age.
In men, one study found that aromatase inhibition with Arimidex did not negatively affect kinetically measured bone calcium turnover or indirect markers of bone calcium turnover, at least in the short term [2].
While short-term use does not appear to result in extreme changes in bone strength, many male users report increased bone and joint pain when estrogen is well below normal physiologic levels due to Arimidex use.
This bone and joint pain invariably subsides when Arimidex is discontinued or when the Arimidex dosage is adjusted to allow estrogen levels to return to normal physiologic levels.
Fatigue.
Similar to bone and joint pain issues in anabolic steroid users who lower their estrogen levels too much, persistent fatigue is also a common reported Arimidex side effect.
This is the result of estrogen levels becoming too low, as mentioned earlier.
Estrogen is well known to play an important role in the proper functioning of the central nervous system (CNS), and when it is reduced below normal physiological levels through aromatase inhibitors, it can lead to chronic fatigue, a symptom that can only be adequately treated by restoring circulating estrogen levels to normal.
Negative effects on cholesterol
This is a side effect common to all aromatase inhibitors or any substance that reduces total circulating estrogen levels in the body.
Arimidex side effects are no exception, and this is probably the most important side effect to understand.
This side effect is also why we emphasized controlling estrogen levels rather than eliminating them completely in this profile.
Estrogen is known to play a very important role in the liver, where it works to produce good cholesterol levels (increasing HDL, the good cholesterol, and decreasing LDL, the bad cholesterol).
When estrogen levels decrease below normal physiologic levels, cholesterol changes occur, resulting in a decrease in good cholesterol (HDL) and an increase in bad cholesterol (LDL), which increases the risk of cardiovascular disease (CVD).
In one study, 300 mg of testosterone enanthate per week for 20 weeks without the use of an aromatase inhibitor resulted in a 13% reduction in HDL cholesterol, and when the testosterone dose was increased to 600 mg per week, the reduction in HDL cholesterol was further increased to 21% [3].
Thus, the data examined shows a very clear increase in estrogen through aromatization and hepatic metabolism, which actually helps to offset the negative cholesterol changes caused by supraphysiological amounts of anabolic steroid use.
This is not surprising considering that estrogen itself is known to have a positive effect on cholesterol levels.
Therefore, the use of aromatase inhibitors and their impact on the cholesterol profile should always be kept in mind by any user considering the addition of an aromatase inhibitor during a cycle or for PCT.
It is recommended to use the lowest dose of an aromatase inhibitor during a cycle with the goal of controlling estrogen rather than eliminating total estrogen levels.
The idea in this case is to keep estrogen levels within a normal range, preventing them from spiking due to aromatization, while at the same time preventing them from dropping to near zero due to the use of a full dose of an aromatase inhibitor.
Estrogen Rebound
This is one of the very important Arimidex side effects to understand.
It is a side effect commonly seen with both Arimidex and Letrozole (Femara).
Aromasin (Exemestane), the third major aromatase inhibitor, does not show estrogen rebound.
This is because Arimidex and Letrozole are known as non-lethal aromatase inhibitors.
Aromasin (Exemestane) is a suicidal aromatase inhibitor.
Suicidal aromatase inhibitors (such as aromasin) bind to and inhibit the aromatase enzyme, which means that the inhibited enzyme permanently binds to the aromatase, rendering the enzyme inactive forever.
The body will eventually produce more aromatase enzyme, but the currently bound enzyme will remain bound indefinitely and there is no risk of estrogen rebound.
However, non-lethal aromatase inhibitors, such as Arimidex and Retro, are only bound to the aromatase enzyme for a limited time before natural metabolism or competition from other substrates causes the aromatase inhibitor to unbind.
If a non-lethal aromatase inhibitor is discontinued too abruptly, circulating inhibited aromatase enzymes that have not been metabolized in vitro will become free again and begin to aromatize androgens to estrogens at a rapid rate.
Therefore, it is recommended to slowly reduce the dose and/or number of doses when tapering or discontinuing Arimidex.
Medical References
[1] “Switching postmenopausal women with endocrine-responsive early breast cancer to anastrozole after 2 years of adjuvant tamoxifen: combined results of the ABCSG trial 8 and the ARNO 95 trial”. Jakesz R, Jonat W, Gnant M, Mittlboeck M, Greil R, Tausch C, Hilfrich J, Kwasny W, Menzel C, Samonigg H, Seifert M, Gademann G, Kaufmann M, Wolfgang J (2005). The Lancet 366 (9484): 455-62. doi:10.1016/S0140-6736(05)67059-6. PMID 16084253.
[2] Estrogen suppression in men: metabolic effects. Mauras N; O'Brien CO; Klein CO; Hayes V. J Clin Endocrinol Metab. 2000 Jul;85(7):2370-7 (ISSN: 0021-972X)
[3] Testosterone dose-response relationship in healthy young men. Bhasin S, Woodhouse L. et al. Am J Physiol Endocrinol Metab 281:E1172-81, 2001
