Has he started puberty? My nephew (not on ADHD meds) was still around 5'2 at age 15 - now he's 18 and is close to 6 feet - puberty didn't kick in until 16 or so. My brother had the same puberty and growth pattern, he is over 6 feet.

ADHD meds do suppress your appetite, but I don't think there is much evidence that they stunt growth.

I'm only familiar with ADHD meds through my DH and SS. DH took ADHD meds - probably starting around the same age as your SS - there were limited options back then so he took the same medication until he went to high school and refused to take it any more because it made his hands shake. He now takes a different medication. SS has taken many different meds (In my opinion, I don't think he has ADHD and that's why the meds don't work they way everyone expects them, too. I think they decided he has ADHD because he was difficult and DH has it, but he doesn't act like DH at all.). Neither one's appetite was ever impacted - both are big eaters and always have been. DH was also always taller than average. He was over 5 feet probably in 1st or 2nd grade, looking at pictures of him from childhood. He was taller than MIL, who is around 5'4", 5"5" by the time he was 9 and he is now very tall (think NBA tall). SS is short considering DH's height, but still likely in the normal range for his age. 

You could try changing his medication to see if that helps. Does he see a specialist about his ADHD? 

Could it also be a control thing? Does he get lots of attention about eating? Does he have favorite foods or snacks? When he's eating those, does he eat more? 

Yes, DH needs to talk with the doctor first.  And I had friends in middle school through high school, mostly boys, who remained small unitl they were OUT of high school! 

What about milkshakes, smoothies?  Will he eat those?  You can pack lots of calories into those and even make them dairy free if needed. 

I understand the food issues, however, as the SM I have zero control; I've been through the worst of it with a selective eating disorder skid.  YSD is now getting pickier too - DH gets to deal with the food.

Talk to the men in your family and find out how they processed thru puberty. DH was a skinny boy when he graduated and didn't finish growing until his early  20's. He will have to learn to feed himself. Maybe some protein shakes would help him get better nutrition.  Something he can mix up himself to his tastes.  Macho weightlifting guys use protein powder all the time. It's not girly at all. It might appeal to your SS. 

Talk to the men in your family and find out how they processed thru puberty. DH was a skinny boy when he graduated and didn't finish growing until his early  20's. He will have to learn to feed himself. Maybe some protein shakes would help him get better nutrition.  Something he can mix up himself to his tastes.  Macho weightlifting guys use protein powder all the time. It's not girly at all. It might appeal to your SS. 

My SS is the same age and also has ADHD. We had him on meds for about a year when he was 9-10 but the negative side effects weren't worth it so we took him off. He's a big eater but very skinny, probably due to the hyperactivity as he's constantly bouncing around. His father is quite thin too so it's probably partially genetic.

I've heard of meds stunting appetite but not growth. SS is only about 5-5'1 as well, and he's average compared to his peers. As for puberty, I think that can kick it later for a lot of boys anyway. SS still has a young voice and a tiny bit of upper lip hair that he's very proud of. lol. 

SS is also an extremely picky eater, which is part of ADHD and part of being a kid I think. You should confirm with his pediatrician of course, but he sounds ok to me.

It's probably just his size right now. DH can talk to his doctor if he is concerned. I'm almost 5'9", one brother is 6ft and my younger brother is the same height as me. Our parents are 6ft and 5' 6". SS15 buddies pretty much only hang out at our house and they are a variety of heights. Over 6ft to 5ft. SS16 was on/off adhd meds for a long period of time. I don't think his growth is stunted. He's 5'10. SO is 6' 3" and BM same height as me. I remember when I was a teenager I didn't see one of my brothers friends for a few months and the next time I saw him he was literally 6/8inches taller. They are at a weird age right. 

DH is 6'4". SS15 is about 5'8" or 5'9".  Could still be growing but will probaby not reach his genetic height (his mother is around 5'8" and his 3 older sisters are between 5'8" and 5'10"). I think that medication stunts growth permanently. Yes it temporarily suppresses appetite but I think it has a short half life so it isn't around the clock. I think he takes Vyvanse.  

It could be loss of appetite and it could just be who he is. DH's dad was 6'2 and DH is only 5'9. My mom is 5'10 and I am 5'0. 

There are other supplements besides pediasure. Maybe it is just finding something he likes. Talk to the doctor and maybe order some blood work to see where he is for nutrient levels. He might be totally fine. If you think about what we are actually supposed to eat vs. portion sizes that many of us are used to, we should all be eating kids meals and even that is more than most adults actually need. Then ask for a referral to talk to a nutritionist. 

My sister is on ADHD meds and lost so much weight, the doctor cut back her dosage. It definitely diminished her appetite.

Logically a suppressed appetite would have impact on physical stature.  Less caloric intake and nutritional resources would result in smaller the individual. Some of this may be corrected by late growth spirts associated with increased caloric and nutritional intake.

Just my thoughts of course.