Welcome to NeuroTalk!
I agree with Chemar.... See if you can get him to take it when he first wakes up. The stomach should empty within 20 minutes with just water in it. It is not super critical on an empty stomach.
But with a huge fatty meal that wouldn't empty for hours.. and could break down by then.

I am not sure SAMe will work for you for him. It has been my experience that younger people get irritable on it. SAMe is more effective in the older patient who is getting neurotransmitter let down.

If you really want to try it, don't go over 200mg a day for a month. Usually by the end of the first or second week, you'll see the anxiety or irritability starting if it is going to happen. It can cause hyper behavior and insomnia, and needs to also be taken on an empty stomach with water. (it is also enteric coated).

To increase serotonin, l-tryptophan is available now, and could be used instead of the 5-htp. It is a bit gentler and slower than 5-htp, if he has reactions to the 5-htp.

Watching the sugar intake, especially fructose will help too.
Mood swings with sugar crashes are very confusing and sometimes just getting rid of the sugar will fix some mood issues. (no sugared sodas, or fruit drinks to start).

You've come to the right place. There are many of us who have done natural nutrients for neuro problems. My son has ADHD and did well on fish oil, magnesium and Bcomplex. He was able to get rid of all his Ritalin!

P.S... if you get timed out making a long post here, you can avoid that by checking the little box, "remember me" when you log in. Then the time limit is not active any more and you won't lose your work.