Although I am usually not inclined to posit speculations on why a particular drug does or doesn't do something, in this case I will. Im guessing that the higher doses of Anadrol cause enough appetite suppression (at least anecdotally) to make eating rather difficult. It can also increase insulin resistance and glucose intolerance (5). This has the effect of making macronutrient absorption more inefficient, and could also be a factor in reducing gains when the dosage goes over 100mgs/day. Unfortunately, Anadrol also has a reasonably profound effect on your body's natural hormonal system, on par with most other oral steroids , but not as bad as most injectables, and its certainly not as harsh on your lipid profile as many anabolics are
These types of steroids are generally made by non-licensed manufacturers and are not overseen by any regulatory board. Due to it becoming increasingly harder to obtain pharmaceutical grade steroids, most people opt for underground brands. The main problem with underground brands is no one knows what type of environment these steroids are produced in. They may or may not be produced in a sterile environment. There are however many big underground brands available that have hundreds of positive reviews, it is always best to stick with the big brands.