Neuroimaging, Omega-3 and Reward in Adults With ADHD (NORAA) Trial

Background: \- People with attention-deficit hyperactivity disorder (ADHD) often have problems with motivation and rewards. . Omega-3 fats have helped symptoms of ADHD improve in children. Researchers want to learn more about the brain activity of people with ADHD and see how taking omega-3 fats might help. Objective: \- To learn more about how omega-3 fats affect brain activity and ADHD symptoms. Eligibility: \- Adults age 18 55 with ADHD symptoms. Design: * Participants will be screened with medical history and review of medical records. * For study visit 1, participants will have a medical examination and be interviewed to confirm they have ADHD. They will have an IQ test and give blood and urine samples. Height, weight, and blood pressure will be measured. They will also need to sign consent to agree to take part in the study. They will be asked to complete a food diary for 4 days * For visit 2, participants will give a blood sample. They will complete questionnaires about their mood and ADHD symptoms.. They may give a blood or saliva sample for genetic testing. * Participants will have a magnetic resonance imaging (MRI) scan. They will lie on a table that slides in and out of a metal cylinder. It makes loud noises; participants will get earplugs. This scan examines the structure of the brain. * Participants will have a functional MRI scan. This scan measures the function of the brain while the volunteer is performing tasks in the scanner. They will stop ADHD medications 48 hours before this scan. * Participants will receive key-lime flavored omega-3 smoothie mix or placebo to takeevery day * For visit 3, participants will give blood samples and complete questionnaires. * For visit 4, participants will be weighed and have a blood test and MRI scans as per before. They will repeat the questionnaires and will guess whether they received the omega-3 or placebo.