Not the heavy stuff. A friend of mine tried to buy it. I’m pretty sure he was a drug addict as he came with none and I suspect his American doctor(s??) had cut him off. He asked at a pharmacy and they said sorry you have to go to a hospital and see a doctor for that. The doctor said no. I was rather impressed actually. It seems these days that it’s the US, not Thailand, that hands them out like candies. Anyway to answer your question. Don’t check them. That looks like drug smuggling. Make sure it’s very clear that this stuff was prescribed by a genuine doctor. You could call him the Bangkok Hospital near to where you are staying and ask them for very specific requirements.
Yes this advice makes no sense for 23 or 24. Personally I think this topic is all nonsense from Falang advisers who want to make money. Can you imagine any Thai person paying any attention like this? Best to figure out if and when anything happens.