It should be noted that in theory if one was to consistently suppress your natural estrogen levels for a long period of time, this would negatively impact your health, including your cholesterol. Due to the ability of Letrozole- to inhibit estrogen so much, this should definitely be a concern to most users. However the research that has focused on the relationship between use of letrozole and cholesterol levels is rather inconsistent in it's findings. Many studies have concluded that the compound is detrimental to both a user's HDL and LDL cholesterol levels, while other research has found no link. Obviously individuals are best served to monitor their cholesterol while using any compound via blood tests however barring that, letrozole should simply not be run for extended periods of time if at all possible. Doing so could cause serious medical complications.
Along with the issues related to blood lipids is the fact that many users complain that their libido is dramatically reduced when using the compound. This is related to the fact that estrogen is partly responsible for the regulation of an individual's sex drive. Since Letrozole- is so potent it can often drive estrogen levels too low and this inhibits a user's libido. To avoid this users can lower dosages, but some anecdotally report that even extremely low doses of the drug can cause problems. If this is the case a less potent compound such as exemestane or anastrozole may be a more appropriate option.
There are possible estrogenic side effects of Nandrolone despite it not being a very estrogenic hormone, at least not directly. Nandrolone does aromatize slightly. Aromatization refers to the conversion of testosterone to estrogen . This takes place when the testosterone hormone interacts with the aromatase enzyme. When the conversion takes place this can cause estrogen levels to go up, which can promote gynecomastia and water retention. High blood pressure can also become an issue if water retention becomes severe. Along with the low level of aromatase activity Nandrolone is also a progestin and has a strong binding affinity for the progesterone receptor. This may stimulate the mammary tissue and enhance the risk of gynecomastia in sensitive individuals.
Combating the estrogenic side effects of Nandrolone can be achieved by the use of anti-estrogen medications, specifically Aromatase Inhibitors (AI’s) such as Anastrozole ( Arimidex ). Selective Estrogen Receptor Modulators (SERM’s) are also sometimes used, such as Tamoxifen ( Nolvadex ). However, AI’s are the proper choice as they will directly reduce serum estrogen levels and SERM’s will not. An AI should be enough to reduce and avoid gynecomastia unless the individual already has existing gynecomastia that could potentially be exasperated.
Important Note: It’s often been said that Nandrolone based gynecomastia is based on increases in prolactin. It is true that 19-nor steroids can increase prolactin, which can also negatively affect libido and erection function. Some men may need to use a dopamine agonist to combat this. However, it is not prolactin that causes 19-nor based gynecomastia but rather the imbalance between estrogen and progesterone. If you merely combat prolactin you may find yourself with the very gynecomastia you tried to avoid.
Heavy consumption of the essential amino acid lysine (as indicated in the treatment of cold sores) has allegedly shown false positives in some and was cited by American shotputter C. J. Hunter as the reason for his positive test, though in 2004 he admitted to a federal grand jury that he had injected nandrolone.  A possible cause of incorrect urine test results is the presence of metabolites from other AAS, though modern urinalysis can usually determine the exact AAS used by analyzing the ratio of the two remaining nandrolone metabolites. As a result of the numerous overturned verdicts, the testing procedure was reviewed by UK Sport . On October 5, 2007, three-time Olympic gold medalist for track and field Marion Jones admitted to use of the drug, and was sentenced to six months in jail for lying to a federal grand jury in 2000.