People do not agree about the diagnosis of ADHD. The number of people with ADHD has increased in the last several years. Some people think this is because doctors are diagnosing too many people. Others think it is because doctors are getting better at finding people with ADHD. Some people think that ADHD is made-up and not a real illness, even though it's the most researched condition in psychiatry. Most studies suggest that ADHD is mostly caused by problems with genes.