Marcus: How ADHD affects me and why being different is good
Marcus has autism and ADHD. Symptoms of ADHD include inattentiveness, hyperactivity and impulsiveness.
He says some of the things people get wrong about ADHD are "we're just naughty, and obnoxious and don't listen at all".
He says these views can be quite "upsetting", but he sees ADHD as his super power.
Watch Marcus, who is an ADHD Foundation Young Ambassador, tell Newsround about how ADHD affects him and how his service dog Cocoa helps him