Health problems. Lots of things that can go wrong here but I wont bother to go into too much detail because you have heard it all before. These problems are very dosage dependent and drug dependent. Enlargement of the heart is probably the biggest problem. Although enlarging your heart sounds like a good thing, its very, very bad and is what leads to heart attacks in young bodybuilders. Damaging your kidneys and liver is another relatively common problem as the body works overtime to filter out stuff that it doesnt want. Then there is the problem with natural testosterone production being shut down.
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
Like all great innovators, Dan paid a price for thinking differently. But it's never the people who "aim to please" that make a difference. It's always the men who stick their necks out and take risks that make the discoveries for future generations to remember. There's an old saying, "No one ever erected a monument to a committee." In other words, it's the individual who's important, the lone voice of reason and madness who breaks the rules and reassembles them in a way that makes it impossible for people to ever view things in quite the same way. Dan Duchaine is such an individual. It's irrelevant whether you think his contributions have been mostly positive or negative. He has forever changed bodybuilding.