What is anastrozole?

Anastrazole is a prescription treatment that works by blocking the aromatase enzyme.  This enzyme converts testosterone to estradiol (the primary form of estrogen).  Anastrozole is not FDA-approved for low testosterone treatment but is used “off-label” by physicians. Off-label prescribing is the term used when a physician prescribes a medication for a specific condition different than the condition the medication was originally approved for. Off-label prescribing is common and approximately 20% of all prescriptions are done off-label. We only use medications off-label when there is high-quality safety and efficacy evidence available.  

Why is anastrozole part of my treatment regimen?

Your Nimbus Hormone test indicated that estradiol levels were elevated due to increased aromatase activity. Aromatase activity and thus estradiol levels increase as we age and as our body adipose tissue percent increases.1

Is anastrozole effective for restoring normal testosterone levels?

Anastrazole affects testosterone levels in two distinct ways.  By lowering circulating estrogen levels, anastrozole causes an increase in LH (Luteinizing Hormone) which is the hormone responsible for telling the testes to produce testosterone. 

The second effect is by suppressing the conversion of testosterone to estrogen.  Anastrazole will decrease the estradiol/testosterone ratio by approximately 77%, meaning more testosterone is available to the cells in the body.2

Are there potential side effects from using anastrozole?

The adverse effects of anastrozole therapy occur when estrogen levels are too suppressed.  Estrogen has several different effects in men, including maintaining bone density and several aspects of sexual health, prostate health, and metabolism.3  At Nimbus, we monitor estradiol levels during therapy and adjust anastrozole dosage if estradiol levels are too low.  Other adverse effects that have been reported include stomach upset, bone pains, mood disturbances, and fluid retention.


  1. Benjamin Z. Leder, Jacqueline L. Rohrer, Stephen D. Rubin, Jose Gallo, Christopher Longcope, Effects of Aromatase Inhibition in Elderly Men with Low or Borderline-Low Serum Testosterone Levels, The Journal of Clinical Endocrinology & Metabolism, Volume 89, Issue 3, 1 March 2004, Pages 1174–1180,
  2. de Ronde W, de Jong FH. Aromatase inhibitors in men: effects and therapeutic options. Reprod Biol Endocrinol. 2011;9:93. Published 2011 Jun 21. doi:10.1186/1477-7827-9-93
Hammes SR, Levin ER. Impact of estrogens in males and androgens in females. J Clin Invest. 2019;129(5):1818-1826. doi:10