I still get phenergan flashbacks.
Back in the 70s the family GP suggested it to my parents to deal with my small person insomnia. (Or not going to bed and actually sleeping when required to. I wasn't diagnosed with ADHD until this year, and at nearly 50 years old I finally understand why I am not so great at sleeping in demand).
I must have been between 5-9 in the years when they used it. It was horrible. My mind would be racing, but in a weird, strange way. But my body wouldn't respond and let me move away from the things my imagination was producing. I'm sure it felt worth it to them, mostly cos they kept using it. But bearing in mind the profound fear it induced in me, I think it was accidentally abusive.
I guess the one upside is I have never taken any recreational drugs. The thought of going back to the state of mind going off and creating weird shit, while my body can't do anything about it cos it's mostly paralysed, sounds like as much fun as being held under water for a joke.
Whatever a parent gain in using phenergan on their children, it is worth bearing in mind that the passive, drowsy child they see may be hallucinating and struggling with scary, trippy images ... while unable to demonstrate their fears and distress physically.