? for pharm ladies

So Nicholas is starting a new med that I havent gotten to discuss in length with his Dr yet. I am comfortable w/ him being on it and I know it is really commonly used for RSS kids but I was hoping you all might be able to give me some more insight before my next appt with his GI dr. So the med is Periactin-- I know a common side effect is drowsiness. Is the drowsiness temporary and will go away as he gets used to the med or is if it makes him drowsy once it will always make him drowsy?

He is taking this for appetite stimulation and we were told to give it to him 3x/day 30 mins before eating and have him on it for 3 weeks then off for a week. Is this med something that can sort of jump-start his own appetite to increase or is it something that will only increase his appetite when he is taking it? I know they said they want him to have the week off to monitor how well and if it is working so they can adjust his dosage. Will he end up needing to be on this forever? Just a few questions, not even sure if a pharmacist can answer these but thought it was worth a shot since his GI is kind of hard to get ahold of. TIA!