Cyproheptadine/Periactin is very commonly prescribed with ADHD medication, when stimulants significantly impact appetite but help with ADHD symptoms overall. My son took it for a couple years when he hadn’t gained an ounce in 2 years. He gained 12 lbs the first year on it, if I remember right. It was a huge help. Once he hit puberty, he eats like a horse non-stop and appetite is no longer an issue (on the very same medicine), now we have the opposite weight problem.
According to this article, it can also help with sleep issues:
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism