I'm sure that there is some degree of doping in football, a game that generates that kind of wages gives huge incentives to reach the top of the game, with any means necessary. I doubt that any top club, today, have any form of a systematic doping scheme. There might be some individuals doing whatever to be able to claim the golden ticket for themselves and their families.
If by some chance there are top clubs that go around the rules to give themselves an advantage, I believe all top clubs are doing the same. There's zero chance that Liverpool is doing some under the table stuff without other clubs either knowing or doing the same.
City was accused of doping when they walked the league, Liverpool accused after two 90+ point seasons, Leicester when they won the league after running every team into the ground, and I'm sure there was plenty of accusations towards us after dominating the league for decades.
We have massively improved our running/sprinting in games after Ole took over from Mou, and I doubt that have anything to do with doping, in the same sense that I doubt that Liverpool's' two 90+ seasons had anything to do with doping. I'm looking forward to when the doping accusations are pointed towards us again, the "paying of refs/FA" is finally starting to come back and it's a sure sign that we are rattling some trees.