Yes, the longer you are on the more it takes to get a response. That's why you are seeing the doses you see these days on the boards. These guys in this thread that need a cruise dose of 600 mg/w is an example of not responding well anymore. Their AAS run is in the 2-4 grams a week range. That is a lot. There is a video out aof Ryan Kenelly former powerlifting world record guy. He describes how he had to up the dose more and more as his body became resistant to the drugs to the point he was spooning raw oral powders in his mouth.
Any studies to back this up?
Cause according to this line of thought any TRT patient that has been on TRT for years would have to consistently up their dose to remain in the same acceptable testosterone range and that is simply not true.