Research Review
Issues With Using Tamoxifen For Bodybuilding

Issues With Using Tamoxifen For Bodybuilding

Issues With Using Tamoxifen For Bodybuilding



We get an almost daily question where customers ask us what we suggest for PCT, and how the person in question has been told by everybody they must use a prescription breast cancer drug called Tamoxifen (sometimes sold under the brand name Nolvadex), to ensure they retain their muscle gains and prevent potential problems with gynecomastia. This article will go into some of the details on why Tamoxifen has been recommended for bodybuilders, as well as some side effects that most people fail to understand before embarking on the use of this compound.

What Does Tamoxifen Do?

Tamoxifen is classed as a specific estrogen receptor modulator or SERM. It acts as an estrogen antagonist in the brain and the breast area meaning it prevents estrogen from exerting its normal effect in those areas. With respect to its action in the brain it inhibits the conversion of testosterone to estrogen which during a cycle can mean that estrogen levels remain low. Although low estrogen is often considered advantageous by bodybuilders it should be noted that estrogen helps both with the accrual of muscle mass and also helps to boost libido on cycle. In fact, when bodybuilders use testosterone enhancing compounds and run tamoxifen alongside it, they often lose out on some of the muscle gains and enhanced libido that normally accompanies testosterone elevation.

Tamoxifen dosage used in bodybuilding

Nolvadex is typically taken at 40mg per day for the first 2 weeks of a PCT, and then reduced to 20mg daily for the final 2 weeks. Despite this, PCT is not something that is 'one size fits all' and Tamoxifen might not be the right choice for everyone. 

Negatives Of Tamoxifen Use

Although classed as an estrogen antagonist it should be noted that in some parts of the body tamoxifen actually acts as an estrogen agonist meaning it actually acts in an estrogenic manner as opposed to how most think of it being which is an anti-estrogen. When it acts in an estrogenic fashion in the liver for instance, tamoxifen can increase levels of sex hormone binding globulin (SHGB) which acts to bind to testosterone thus lowering free testosterone in the body. Free testosterone is the amount of unbound testosterone in the system and it is the level of free testosterone which is strongly correlated to the positive effects of high testosterone such as increased muscle mass, strength, and libido.

By lowering free testosterone, tamoxifen has the potential to hurt our bodybuilding gains. This helps to explain why we never hear of people using tamoxifen on a standalone basis (similar to how a testosterone booster is used) and gaining any muscle mass despite the significant rise in testosterone it is capable of producing. Quite simply, a lot of the testosterone rise is cancelled out by the increase in SHGB. Another negative of tamoxifen's action in the liver is its ability to suppress production of the peptide hormone IGF-1. IGF-1 is broken down from growth hormone and is considered to be more potent than growth hormone itself for the purposes of building muscle tissue. High IGF-1 levels make a big contribution to the process of building a better physique and the ability of tamoxifen to suppress IGF-1 levels is another reason why tamoxifen use tends to be disappointing for the purposes of building muscle mass.

In fact, a recent study which showed a rise in total testosterone (they failed to measure free testosterone or levels of SHGB) and a reduction in IGF-1 levels after tamoxifen usage is a significant indicator as to why it can prove disappointing for the building or maintenance of muscle mass.(1,2) The fact that tamoxifen is referred to as an anti-estrogen overlooks the fact that outside of certain tissues it promotes estrogenic effects. A study published in the Journal of Endocrinology(3) showed that long term tamoxifen use increased serum testosterone levels by 50% which is certainly a healthy increase. However, at the same time serum estrogen levels increased by a massive 341%. In fact, in the control group in this study, which only used tamoxifen for a week, estrogen rose after just four days. Considering that the subjects in this trial used tamoxifen at a lower dose of just 10mg it begs the question of what would happen if used at the higher dosage typically seen in bodybuilding circles.

Tamoxifen and gyno in bodybuilders

Tamoxifen is of course frequently used to suppress estrogenic action in breast tissue to prevent gynecomastia for which it can work rather well during cycle. It will not totally eliminate the possibility of gyno though especially with those steroids that act in a progesterogenic fashion for which something that lowers prolactin such as the supplement Vitex will be required. Assuming though that your cycle went well and you ran a PCT and you battled through the suppressed sex drive, low IGF-1 levels and low free testosterone levels seen with tamoxifen usage. What happens when you remove tamoxifen? If we consider the study above which shows a profound rise in estrogen in the body during tamoxifen use, its removal is going to create a situation where we now have high estrogen levels in the body and with nothing to stop this estrogen from causing gyno in male bodybuilders. This creates a recipe for the kind of rebound gyno that you often hear people complaining about on bodybuilding forums. Adding insult to injury, high estrogen levels are suppressive in their own right which can cause delayed progress in the gym when coming off tamoxifen use.. 

Other Health Effects

Carcinogenic action - Tamoxifen has been shown in several studies 4,5,6) to increase the risk of cancer and is listed as a known carcinogen by the American Cancer Society. A 2006 study in The Lancet showed it increased mortality rate in women using tamoxifen. Studies in rats (7) add further weight to the argument supporting tamoxifen's carcinogenic potential with up to 80% of animals developing malignant tumours.

Liver damage - Tamoxifen has been studied for its effects on liver for some time with it being linked to fatty liver in women (8) as well as showing an increased likelihood in the formation of liver cancer.

Cataracts - Tamoxifen is acutely toxic to the eyes with more than one report on a bodybuilding forum showing a user who irreversibly damaged their eyesight. Studies (9,10) support the notion that tamoxifen can contribute to increasing susceptibility to cataracts.

Blood Clots - Tamoxifen usage is recognised as increasing the risk of blood clotting which if it occurs in a major artery or cardiac tissue can potentially be life threatening. For bodybuilders whose blood pressure may be high it makes tamoxifen use doubly dangerous.

Low libido - As previously noted the negative impact on free testosterone levels of tamoxifen can cause users to fail to experience the effects associated with elevated testosterone including libido. Compared to other compounds which increase testosterone, tamoxifen users tend to report poorer libido. In addition, the adverse effect on blood clots means it can make erectile dysfunction more likely as well. It is for this reason that many users will employ a testosterone booster in PCT to help address these shortcomings of tamoxifen usage.

Mood swings - Perhaps the most common complaint of all from bodybuilders using tamoxifen or other SERM's during PCT is they cause unbearable mood swings with frequent reports of tearfulness, and depression occurring among bodybuilders. While not everyone gets this it is notable that these effects don't get reported to anywhere the same extent with other PCT products making it feasible that this occurs as a consequence of the rise in serum estrogen seen during tamoxifen use.

Final thoughts on Tamoxifen for PCT

While many bodybuilders see tamoxifen as an essential hopefully this article helps to illustrate some of the potential negatives associated with its use. While it can be important in particular situations especially if used during cycles of aromatising compounds, it's overuse and usage in pct can cause a host of issues. A more sensible strategy for prohormone or AAS users is to employ the use of an aromatase inhibitor to lower estrogen levels significantly, making an SERM less important, as well as addressing other aspects of PCT which are commonly overlooked and discussed in our article on post cycle therapy. Finally, the use of aromatising products should be limited and if these are going to be used an AI as opposed to an SERM is a much better solution for managing estrogen levels on cycle. For those who insist on using tamoxifen during PCT it is important this is combined with an AI to help mitigate against the prospect of rebound gyno which could potentially occur with tamoxifen use. In addition the use of a testosterone booster to help combat the deleterious effects of tamoxifen on libido and mood is advisable with the use of a product such as Activate Xtreme a good tool to address both this aspect and also to boost free testosterone levels which are otherwise suppressed during tamoxifen use.

Recommended Products


Post Cycle Matrix

Formestane Max



  1. Birzniece V. (2012): Gender differences in the neuroendocrine regulation of growth hormone axis by selective estrogen receptor modulators.
  2. Colletti R (1989): Effect of Tamoxifen on Plasma Insulin-like Growth Factor I in Patients with Breast Cancer
  3. Willis KJ : Hormonal effects of tamoxifen in Oligospermic men
  4. Fisher,B., Costantino,J.P., Redmond,C.K., Fisher,E.R., Wickerham,D.L., Cronin,W.M. and other NSABP contributors (1994) Endometrial cancer in tamoxifen-treated breast cancer patients: findings from the National Surgical Adjuvant Breast and Bowel Project
  5. IARC (1996) IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Some Pharmaceutical Drugs. IARC Scientific Publications, Vol. 66, IARC, Lyon.
  6. Bergman,L., Beelen,M.L.R., Gallee,M.P.W., Hollema,H., Benraadt,J., van Leeuwen,F.E. and Comprehensive Cancer Centres' ALERT Group (2000) Risk and prognosis of endometrial cancer after tamoxifen for breast cancer. Lancet, 356, 881–887.
  7. Greaves,P., Goonetilleke,R., Nunn,G., Topham,J. and Orton,T. (1993) Two-year carcinogenicity study of tamoxifen in Alderley Park Wistar-derived rats.
  8. Ogawa Y (1998): Tamoxifen-induced fatty liver in patients with breast cancer 9. Paganini-Hill (2000): Eye problems in breast cancer patients treated with tamoxifen.
  9. Zhang (1994): Tamoxifen blocks chloride channels. A possible mechanism for cataract formation.

Want To Learn More?
Get the Latest Articles from Predator Nutrition delivered every week!

Sign up to our exclusive newsletters and be the first to know about best new articles. Please enter your email address and when you are done simply press Subscribe.