We place a lot of trust in medical professionals. Your doctor gives you a prescription for something - for most people, you take it on the assumption they know what they're doing. (Yes, I realize there's likely a sub-contingent of the HN crowd that Googles everything they take -- but there was no Google back then, and particularly not in East Germany, where almost all of the information you got was carefully controlled). Witness how easy it was for Larry Nassar to perpetuate years of abuse against over 250 children, and that's today in the US.
Even if the trust was simply "hey, this will help you perform better and it's safe", and the "it's safe" part is a lie, it's still abuse. And the things described in the article are actually far worse than just that.
I've only taken high-dose steroids for a medical condition once. I could tell at the higher levels, but not much at the lower levels. If someone started off slow and slowly increased the dosages, it is quite possible that it would be missed. And that's with adults, not necessarily children.
I defiantly knew what the effects where - you feel like you can run though walls and pushes your aggression through the roof.
We are both lucky to not have been lied to and have the internet. Pre-internet and the doctor telling me the vitamins do that? I'm not sure I could have known any differently without some knowledge of this stuff as an adult, and agreed - not as a child either.