From your experience , can a person who has add study to become a doctor or an engineer ? or he'll have problems despite taking medications ?

Yes, it depends...: Yes, many with add can study for professions requiring focus ; discipline but won't be successful unless they find effective treatment. Medications can help but there are many other effective treatments including dietary modifications, nutritional supplements, herbs meditation, exercise ; homeopathy. See http://blog.Naturalhealthyconcepts.Com/2012/07/02/treat_add_and_adhd_naturally/.

Agree w Dr. Baker: A patch work quilt approach often proves to be the best way to address ADHD. Deep breathing, yoga, exercise programs, pharmacotherapy, learning organizational skills, cognitive behavioral therapy, cranial electrotherapy stimulation & acupuncture are some options.