Dienogest was synthesized in 1979 in Jena , Germany under the leadership of Prof. Kurt Ponsold, was initially referred to as STS-557 .   It was found that its potency was 10 times that of levonorgestrel .  The first product on the market to contain dienogest was a combined oral contraceptive pill (with ethinylestradiol), Valette, introduced in 1995 and made by Jenapharm .  In 2007, dienogest was introduced as Dinagest in Japan for the treatment of endometriosis, and it was subsequently marketed for this indication as Visanne in Europe and Australia in December 2009 and April 2010, respectively.  Qlaira was introduced in Europe in 2009 and Natazia was introduced in the United States in 2010. 
I have somewhat extensively studied DNP prior to, during and after my own experiments with this incredibly enticing poison. Surely you didn’t think I was writing all this based on sheer conjecture, hypothesis, and study? There is also some great DNP dialoguing within my Steroid .com signature.
No matter how safe you hear a given herb, chemical, or drug (regardless of dosage) is there is always the possibility of individual sensitivities. This issue becomes greatly magnified with regard to poisons because of the potential for serious injury and fatality. Even the name Di-NITRO-phenol is remarkably engaging to a gear user and “no” proper administration without pre-existing hypersensitivities won’t kill you, but it does all come down to a single truth. A truth you may have arrived at prior to the halfway mark in this piece, the same truth that the author of a great documented journey through the DNP experience, ‘The Inferno: My Week on DNP’ (http://-/portal_includes/articles/2006/06-068-), Vets and Hall-of-Famers like Marcus, Nark, Giant, Booz - just ask them, myself (magic32) and numerous others have come to realize…
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.