I’ve done the rounds of the meds since being diagnosed as an adult. I’m settled (ish) on a combination of a non-stimulant (atemoxetine) and a stimulant (medinkinet) now. I didn’t get nausea with the medikinet but I did experience it (along with quite a few other side effects) with the atemoxetine. Try having some protein before taking it (I have Greek yoghurt or eggs) and treat it a little like morning sickness. If he’s not been taking it for long, you may find the side effects settle down after a while.
Is it the instant or extended release? They do work differently. Also make sure he’s not having vitamin C/acidic drinks while the meds are working as some people find it counteracts the effects.
Look out for the bounce back in behaviour as it’s wearing off, I (and my son) have a definite dip in mood and issues with emotions and fatigue as it wears off, which is hard to deal with sometimes.
I find the medikinet works very well for focus but doesn’t help me with stability in mood, which as a parent is something which was a real problem for me. The longer-acting non stimulant has really grappled to establish a baseline emotionally so the wearing off of the stimulant is not so hard to handle.
I’m still learning about how my ADHD affects me, and have found educating myself to be as useful as the medication, if I’m honest. Dr Russell Barkley and the “how to ADHD” channel on YouTube are both very good.
Exercise is key too, and I take a range of supplements to help as well. Happy to answer any questions about my own experience. ADHD is hard - both to experience, and to be around.