Are there any specific effects or side effects when taking ADHD medication?

I once cautiously spoke to a friend's son because, in my opinion, he showed symptoms of ADHD.
I couldn't say anything more because you denied it until the very end, but it's so unfortunate that you are causing harm to others as well.

These days, many children and adults are experiencing ADHD symptoms. Will their condition improve significantly with medication?
Are there any side effects from the drug treatment?