Attention Deficit Hyperactivity Disorder (ADHD)
What is attention deficit hyperactivity disorder?
What are the symptoms of ADHD in children?
What Causes ADHD?
How is ADHD diagnosed?
How can I work with my child’s school?
Can adults have ADHD?
What efforts are under way to improve treatment?
Attention deficit hyperactivity disorder (ADHD) is one of the most common childhood disorders and can continue through adolescence and adulthood. Symptoms include difficulty staying focused and paying attention, difficulty controlling behavior, and hyperactivity (over-activity).
ADHD has three subtypes:
- Most symptoms (six or more) are in the hyperactivity-impulsivity categories.
- Fewer than six symptoms of inattention are present, although inattention may still be present to some degree.
- Predominantly inattentive
The majority of symptoms (six or more) are in the inattention category and fewer than six symptoms of hyperactivity-impulsivity are present, although hyperactivity-impulsivity may still be present to some degree.
Children with this subtype are less likely to act out or have difficulties getting along with other children. They may sit quietly, but they are not paying attention to what they are doing. Therefore, the child may be overlooked, and parents and teachers may not notice that he or she has ADHD.
Combined hyperactive-impulsive and inattentive
Six or more symptoms of inattention and six or more symptoms of hyperactivity-impulsivity are present.
Most children have the combined type of ADHD.
Treatments can relieve many of the disorder's symptoms, but there is no cure. With treatment, most people with ADHD can be successful in school and lead productive lives. Researchers are developing more effective treatments and interventions, and using new tools such as brain imaging, to better understand ADHD and to find more effective ways to treat and prevent it.
What are the symptoms of ADHD in children?
Inattention, hyperactivity, and impulsivity are the key behaviors of ADHD. It is normal for all children to be inattentive, hyperactive, or impulsive sometimes, but for children with ADHD, these behaviors are more severe and occur more often. To be diagnosed with the disorder, a child must have symptoms for 6 or more months and to a degree that is greater than other children of the same age.
Children who have symptoms of inattention may:
- Be easily distracted, miss details, forget things, and frequently switch from one activity to another
- Have difficulty focusing on one thing
- Become bored with a task after only a few minutes, unless they are doing something enjoyable
- Have difficulty focusing attention on organizing and completing a task or learning something new
- Have trouble completing or turning in homework assignments, often losing things (e.g., pencils, toys, assignments) needed to complete tasks or activities
- Not seem to listen when spoken to
- Daydream, become easily confused, and move slowly
- Have difficulty processing information as quickly and accurately as others
- Struggle to follow instructions
Children who have symptoms of hyperactivity may:
- Fidget and squirm in their seats
- Talk nonstop
- Dash around, touching or playing with anything and everything in sight
- Have trouble sitting still during dinner, school, and story time
- Be constantly in motion
- Have difficulty doing quiet tasks or activities.
Children who have symptoms of impulsivity may:
- Be very impatient
- Blurt out inappropriate comments, show their emotions without restraint, and act without regard for consequences
- Have difficulty waiting for things they want or waiting their turns in games
- Often interrupt conversations or others' activities
ADHD Can Be Mistaken for Other Problems
Parents and teachers can miss the fact that children with symptoms of inattention have the disorder because they are often quiet and less likely to act out. They may sit quietly, seeming to work, but they are often not paying attention to what they are doing. They may get along well with other children, compared with those with the other subtypes, who tend to have social problems. But children with the inattentive kind of ADHD are not the only ones whose disorders can be missed. For example, adults may think that children with the hyperactive and impulsive subtypes just have emotional or disciplinary problems.
What causes ADHD?
Scientists are not sure what causes ADHD, although many studies suggest that genes play a large role. Like many other illnesses, ADHD probably results from a combination of factors. In addition to genetics, researchers are looking at possible environmental factors, and are studying how brain injuries, nutrition, and the social environment might contribute to ADHD.
Genes. Inherited from our parents, genes are the "blueprints" for who we are. Results from several international studies of twins show that ADHD often runs in families. Researchers are looking at several genes that may make people more likely to develop the disorder.2,3 Knowing the genes involved may one day help researchers prevent the disorder before symptoms develop. Learning about specific genes could also lead to better treatments.
Children with ADHD who carry a particular version of a certain gene have thinner brain tissue in the areas of the brain associated with attention. This NIMH research showed that the difference was not permanent, however, and as children with this gene grew up, the brain developed to a normal level of thickness. Their ADHD symptoms also improved.4
Environmental factors. Studies suggest a potential link between cigarette smoking and alcohol use during pregnancy and ADHD in children.5,6 In addition, preschoolers who are exposed to high levels of lead, which can sometimes be found in plumbing fixtures or paint in old buildings, may have a higher risk of developing ADHD.7
Brain injuries. Children who have suffered a brain injury may show some behaviors similar to those of ADHD. However, only a small percentage of children with ADHD have suffered a traumatic brain injury.
Sugar. The idea that refined sugar causes ADHD or makes symptoms worse is popular, but more research discounts this theory than supports it. In one study, researchers gave children foods containing either sugar or a sugar substitute every other day. The children who received sugar showed no different behavior or learning capabilities than those who received the sugar substitute.8 Another study in which children were given higher than average amounts of sugar or sugar substitutes showed similar results.9
In another study, children who were considered sugar-sensitive by their mothers were given the sugar substitute aspartame, also known as Nutrasweet. Although all the children got aspartame, half their mothers were told their children were given sugar, and the other half were told their children were given aspartame. The mothers who thought their children had gotten sugar rated them as more hyperactive than the other children and were more critical of their behavior, compared to mothers who thought their children received aspartame.10
Food additives. Recent British research indicates a possible link between consumption of certain food additives like artificial colors or preservatives, and an increase in activity.11 Research is under way to confirm the findings and to learn more about how food additives may affect hyperactivity.
How is ADHD diagnosed?
Children mature at different rates and have different personalities, temperaments, and energy levels. Most children get distracted, act impulsively, and struggle to concentrate at one time or another. Sometimes, these normal factors may be mistaken for ADHD. ADHD symptoms usually appear early in life, often between the ages of 3 and 6, and because symptoms vary from person to person, the disorder can be hard to diagnose. Parents may first notice that their child loses interest in things sooner than other children, or seems constantly "out of control." Often, teachers notice the symptoms first, when a child has trouble following rules, or frequently "spaces out" in the classroom or on the playground.
No single test can diagnose a child as having ADHD. Instead, a licensed health professional needs to gather information about the child, and his or her behavior and environment. A family may want to first talk with the child's pediatrician. Some pediatricians can assess the child themselves, but many will refer the family to a mental health specialist with experience in childhood mental disorders such as ADHD. The pediatrician or mental health specialist will first try to rule out other possibilities for the symptoms. For example, certain situations, events, or health conditions may cause temporary behaviors in a child that seem like ADHD.
Between them, the referring pediatrician and specialist will determine if a child:
Is experiencing undetected seizures that could be associated with other medical conditions
Has a middle ear infection that is causing hearing problems
Has any undetected hearing or vision problems
Has any medical problems that affect thinking and behavior
Has any learning disabilities
Has anxiety or depression, or other psychiatric problems that might cause ADHD-like symptoms
Has been affected by a significant and sudden change, such as the death of a family member, a divorce, or parent's job loss.
A specialist will also check school and medical records for clues, to see if the child's home or school settings appear unusually stressful or disrupted, and gather iinformation from the child's parents and teachers, coaches, babysitters, and other adults who know the child well may also be consulted.
The specialist will also ask:
Are the behaviors excessive and long-term, and do they affect all aspects of the child's life?
- Do they happen more often in this child compared with the child's peers?
- Are the behaviors a continuous problem or a response to a temporary situation?
- Do the behaviors occur in several settings or only in one place, such as the playground, classroom, or home?
The specialist pays close attention to the child's behavior during different situations. Some situations are highly structured, some have less structure. Others would require the child to keep paying attention. Most children with ADHD are better able to control their behaviors in situations where they are getting individual attention and when they are free to focus on enjoyable activities. These types of situations are less important in the assessment. A child also may be evaluated to see how he or she acts in social situations, and may be given tests of intellectual ability and academic achievement to see if he or she has a learning disability.
Finally, if after gathering all this information the child meets the criteria for ADHD, he or she will be diagnosed with the disorder.
Currently available treatments focus on reducing the symptoms of ADHD and improving functioning. Treatments include medication, various types of psychotherapy, education or training, or a combination of treatments.
The most common type of medication used for treating ADHD is called a "stimulant." Although it may seem unusual to treat ADHD with a medication considered a stimulant, it actually has a calming effect on children with ADHD. Many types of stimulant medications are available. A few other ADHD medications are non-stimulants and work differently than stimulants. For many children, ADHD medications reduce hyperactivity and impulsivity and improve their ability to focus, work, and learn. Medication also may improve physical coordination.
However, a one-size-fits-all approach does not apply for all children with ADHD. What works for one child might not work for another. One child might have side effects with a certain medication, while another child may not. Sometimes several different medications or dosages must be tried before finding one that works for a particular child. Any child taking medications must be monitored closely and carefully by caregivers and doctors.
Stimulant medications come in different forms, such as a pill, capsule, liquid, or skin patch. Some medications also come in short-acting, long-acting, or extended release varieties. In each of these varieties, the active ingredient is the same, but it is released differently in the body. Long-acting or extended release forms often allow a child to take the medication just once a day before school, so they don't have to make a daily trip to the school nurse for another dose. Parents and doctors should decide together which medication is best for the child and whether the child needs medication only for school hours or for evenings and weekends, too.
Are stimulant medications safe?
Under medical supervision, stimulant medications are considered safe. Stimulants do not make children with ADHD feel high, although some kids report feeling slightly different or "funny." Although some parents worry that stimulant medications may lead to substance abuse or dependence, there is little evidence of this.
Do medications cure ADHD?
Current medications do not cure ADHD. Rather, they control the symptoms for as long as they are taken. Medications can help a child pay attention and complete schoolwork. It is not clear, however, whether medications can help children learn or improve their academic skills. Adding behavioral therapy, counseling, and practical support can help children with ADHD and their families to better cope with everyday problems. Research funded by the National Institute of Mental Health (NIMH) has shown that medication works best when treatment is regularly monitored by the prescribing doctor and the dose is adjusted based on the child's needs.12
Different types of psychotherapy are used for ADHD. Behavioral therapy aims to help a child change his or her behavior. It might involve practical assistance, such as help organizing tasks or completing schoolwork, or working through emotionally difficult events. Behavioral therapy also teaches a child how to monitor his or her own behavior. Learning to give oneself praise or rewards for acting in a desired way, such as controlling anger or thinking before acting, is another goal of behavioral therapy. Parents and teachers also can give positive or negative feedback for certain behaviors. In addition, clear rules, chore lists, and other structured routines can help a child control his or her behavior.
Therapists may teach children social skills, such as how to wait their turn, share toys, ask for help, or respond to teasing. Learning to read facial expressions and the tone of voice in others, and how to respond appropriately can also be part of social skills training.
How can parents help?
Children with ADHD need guidance and understanding from their parents and teachers to reach their full potential and to succeed in school. Before a child is diagnosed, frustration, blame, and anger may have built up within a family. Parents and children may need special help to overcome bad feelings. Mental health professionals can educate parents about ADHD and how it impacts a family. They also will help the child and his or her parents develop new skills, attitudes, and ways of relating to each other.
Parenting skills training helps parents learn how to use a system of rewards and consequences to change a child's behavior. Parents are taught to give immediate and positive feedback for behaviors they want to encourage, and ignore or redirect behaviors they want to discourage. In some cases, the use of "time-outs" may be used when the child's behavior gets out of control. In a time-out, the child is removed from the upsetting situation and sits alone for a short time to calm down.
Parents are also encouraged to share a pleasant or relaxing activity with the child, to notice and point out what the child does well, and to praise the child's strengths and abilities. They may also learn to structure situations in more positive ways. For example, they may restrict the number of playmates to one or two, so that their child does not become overstimulated. Or, if the child has trouble completing tasks, parents can help their child divide large tasks into smaller, more manageable steps. Also, parents may benefit from learning stress-management techniques to increase their own ability to deal with frustration, so that they can respond calmly to their child's behavior.
Sometimes, the whole family may need therapy. Therapists can help family members find better ways to handle disruptive behaviors and to encourage behavior changes. Finally, support groups help parents and families connect with others who have similar problems and concerns. Groups often meet regularly to share frustrations and successes, to exchange information about recommended specialists and strategies, and to talk with experts.
Tips to Help Kids Stay Organized and Follow Directions
Schedule. Keep the same routine every day, from wake-up time to bedtime. Include time for homework, outdoor play, and indoor activities. Keep the schedule on the refrigerator or on a bulletin board in the kitchen. Write changes on the schedule as far in advance as possible.
Organize everyday items. Have a place for everything, and keep everything in its place. This includes clothing, backpacks, and toys.
Use homework and notebook organizers. Use organizers for school material and supplies. Stress to your child the importance of writing down assignments and bringing home the necessary books.
Be clear and consistent. Children with ADHD need consistent rules they can understand and follow.
Give praise or rewards when rules are followed. Children with ADHD often receive and expect criticism. Look for good behavior, and praise it.
How can I work with my child’s school?
If you think your child has ADHD, or a teacher raises concerns, you may be able to request that the school conduct an evaluation to determine whether he or she qualifies for special education services.
Start by speaking with your child's teacher, school counselor, or the school's student support team, to begin an evaluation. Also, each state has a Parent Training and Information Center and a Protection and Advocacy Agency that can help you get an evaluation. A team of professionals conducts the evaluation using a variety of tools and measures. It will look at all areas related to the child's disability.
Once your child has been evaluated, he or she has several options, depending on the specific needs. If special education services are needed and your child is eligible under the Individuals with Disabilities Education Act, the school district must develop an "individualized education program" specifically for your child within 30 days.
If your child is considered not eligible for special education services—and not all children with ADHD are eligible—he or she still can get "free appropriate public education," available to all public-school children with disabilities under Section 504 of the Rehabilitation Act of 1973, regardless of the nature or severity of the disability.
For more information on Section 504 visit the
U.S. Department of Education's Office for Civil Rights
which enforces Section 504 in programs and activities that receive Federal education funds
Department of Education
programs for more information about children with disabilities
Transitions can be difficult. Each school year brings a new teacher and new schoolwork, a change that can be especially hard for a child with ADHD who needs routine and structure. Consider telling the teachers that your child has ADHD when he or she starts school or moves to a new class. Additional support will help your child deal with the transition.
Can adults have ADHD?
Some children with ADHD continue to have it as adults. And many adults who have the disorder don't know it. They may feel that it is impossible to get organized, stick to a job, or remember and keep appointments. Daily tasks such as getting up in the morning, preparing to leave the house for work, arriving at work on time, and being productive on the job can be especially challenging for adults with ADHD.
These adults may have a history of failure at school, problems at work, or difficult or failed relationships. Many have had multiple traffic accidents. Like teens, adults with ADHD may seem restless and may try to do several things at once, most of them unsuccessfully. They also tend to prefer "quick fixes," rather than taking the steps needed to achieve greater rewards.
How is ADHD diagnosed in adults?
Like children, adults who suspect they have ADHD should be evaluated by a licensed mental health professional. But the professional may need to consider a wider range of symptoms when assessing adults for ADHD because their symptoms tend to be more varied and possibly not as clear cut as symptoms seen in children.
To be diagnosed with the condition, an adult must have ADHD symptoms that began in childhood and continued throughout adulthood.15 Health professionals use certain rating scales to determine if an adult meets the diagnostic criteria for ADHD. The mental health professional also will look at the person's history of childhood behavior and school experiences, and will interview spouses or partners, parents, close friends, and other associates. The person will also undergo a physical exam and various psychological tests.
For some adults, a diagnosis of ADHD can bring a sense of relief. Adults who have had the disorder since childhood, but who have not been diagnosed, may have developed negative feelings about themselves over the years. Receiving a diagnosis allows them to understand the reasons for their problems, and treatment will allow them to deal with their problems more effectively.
How is ADHD treated in adults?
Much like children with the disorder, adults with ADHD are treated with medication, psychotherapy, or a combination of treatments.
Medications. ADHD medications, including extended-release forms, often are prescribed for adults with ADHD, but not all of these medications are approved for adults.16 However, those not approved for adults still may be prescribed by a doctor on an "off-label" basis.
Although not FDA-approved specifically for the treatment of ADHD, antidepressants are sometimes used to treat adults with ADHD. Older antidepressants, called tricyclics, sometimes are used because they, like stimulants, affect the brain chemicals norepinephrine and dopamine. A newer antidepressant, venlafaxine (Effexor), also may be prescribed for its effect on the brain chemical norepinephrine. And in recent clinical trials, the antidepressant bupropion (Wellbutrin), which affects the brain chemical dopamine, showed benefits for adults with ADHD.17
Adult prescriptions for stimulants and other medications require special considerations. For example, adults often require other medications for physical problems, such as diabetes or high blood pressure, or for anxiety and depression. Some of these medications may interact badly with stimulants. An adult with ADHD should discuss potential medication options with his or her doctor. These and other issues must be taken into account when a medication is prescribed.
Education and psychotherapy. A professional counselor or therapist can help an adult with ADHD learn how to organize his or her life with tools such as a large calendar or date book, lists, reminder notes, and by assigning a special place for keys, bills, and paperwork. Large tasks can be broken down into more manageable, smaller steps so that completing each part of the task provides a sense of accomplishment.
Psychotherapy, including cognitive behavioral therapy, also can help change one's poor self-image by examining the experiences that produced it. The therapist encourages the adult with ADHD to adjust to the life changes that come with treatment, such as thinking before acting, or resisting the urge to take unnecessary risks.
What efforts are under way to improve treatment?
This is an exciting time in ADHD research. The expansion of knowledge in genetics, brain imaging, and behavioral research is leading to a better understanding of the causes of the disorder, how to prevent it, and how to develop more effective treatments for all age groups.
NIMH has studied ADHD treatments for school-aged children in a large-scale, long-term study called the Multimodal Treatment Study of Children with ADHD (MTA study). NIMH also funded the Preschoolers with ADHD Treatment Study (PATS), which involved more than 300 preschoolers who had been diagnosed with ADHD. The study found that low doses of the stimulant methylphenidate are safe and effective for preschoolers, but the children are more sensitive to the side effects of the medication, including slower than average growth rates.18 Therefore, preschoolers should be closely monitored while taking ADHD medications.19,20
PATS is also looking at the genes of the preschoolers, to see if specific genes affected how the children responded to methylphenidate. Future results may help scientists link variations in genes to differences in how people respond to ADHD medications. For now, the study provides valuable insights into ADHD.21
Other NIMH-sponsored clinical trials on children and adults with ADHD are under way. In addition, NIMH-sponsored scientists continue to look for the biological basis of ADHD, and how differences in genes and brain structure and function may combine with life experiences to produce the disorder.
1 DSM-IV-TR workgroup. The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision. Washington, DC: American Psychiatric Association.
2 Faraone SV, Perlis RH, Doyle AE, Smoller JW, Goralnick JJ, Holmgren MA, Sklar P. Molecular genetics of attention-deficit/hyperactivity disorder. Biological Psychiatry, 2005; 57:1313-1323.
3 Khan SA, Faraone SV. The genetics of attention-deficit/hyperactivity disorder: A literature review of 2005. Current Psychiatry Reports, 2006 Oct; 8:393-397.
4 Shaw P, Gornick M, Lerch J, Addington A, Seal J, Greenstein D, Sharp W, Evans A, Giedd JN, Castellanos FX, Rapoport JL. Polymorphisms of the dopamine D4 receptor, clinical outcome and cortical structure in attention-deficit/hyperactivity disorder. Archives of General Psychiatry, 2007 Aug; 64(8):921-931.
5 Linnet KM, Dalsgaard S, Obel C, Wisborg K, Henriksen TB, Rodriguez A, Kotimaa A, Moilanen I, Thomsen PH, Olsen J, Jarvelin MR. Maternal lifestyle factors in pregnancy risk of attention-deficit/hyperactivity disorder and associated behaviors: review of the current evidence. American Journal of Psychiatry, 2003 Jun; 160(6):1028-1040.
6 Mick E, Biederman J, Faraone SV, Sayer J, Kleinman S. Case-control study of attention-deficit hyperactivity disorder and maternal smoking, alcohol use, and drug use during pregnancy. Journal of the American Academy of Child and Adolescent Psychiatry, 2002 Apr; 41(4):378-385.
7 Braun J, Kahn RS, Froehlich T, Auinger P, Lanphear BP. Exposures to environmental toxicants and attention-deficit/hyperactivity disorder in U.S. children. Environmental Health Perspectives, 2006 Dec; 114(12):1904-1909.
8 Wolraich M, Milich R, Stumbo P, Schultz F. The effects of sucrose ingestion on the behavior of hyperactive boys. Pediatrics, 1985 Apr; 106(4):657-682.
9 Wolraich ML, Lindgren SD, Stumbo PJ, Stegink LD, Appelbaum MI, Kiritsy MC. Effects of diets high in sucrose or aspartame on the behavior and cognitive performance of children. New England Journal of Medicine, 1994 Feb 3; 330(5):301-307.
10 Hoover DW, Milich R. Effects of sugar ingestion expectancies on mother-child interaction. Journal of Abnormal Child Psychology, 1994; 22:501-515.
11 McCann D, Barrett A, Cooper A, Crumpler D, Dalen L, Grimshaw K, Kitchin E, Lok E, Porteous L, Prince E, Sonuga-Barke E, Warner JO. Stevenson J. Food additives and hyperactive behaviour in 3-year-old and 8/9-year-old children in the community: a randomised, double-blinded, placebo-controlled trial. Lancet, 2007 Nov 3; 370(9598):1560-1567.
12 The MTA Cooperative Group. A 14-month randomized clinical trial of treatment strategies for attention-deficit hyperactivity disorder. Archives of General Psychiatry, 1999; 56:1073-1086.
13 Cox DJ, Merkel RL, Moore M, Thorndike F, Muller C, Kovatchev B. Relative benefits of stimulant therapy with OROS methylphenidate versus mixed amphetamine salts extended release in improving the driving performance of adolescent drivers with attention-deficit/hyperactivity disorder. Pediatrics, 2006 Sept; 118(3):e704-e710.
14 U.S. Department of Transportation, National Highway Traffic Safety Administration, Legislative Fact Sheets. Traffic Safety Facts, Laws. Graduated Driver Licensing System. January 2006.
15 Wilens TE, Biederman J, Spencer TJ. Attention deficit/hyperactivity disorder across the lifespan. Annual Review of Medicine, 2002; 53:113-131.
16 Coghill D, Seth S. Osmotic, controlled-release methylphenidate for the treatment of attention-deficit/hyperactivity disorder. Expert Opinions in Pharmacotherapy, 2006 Oct; 7(15):2119-2138.
17 Wilens TE, Haight BR, Horrigan JP, Hudziak JJ, Rosenthal NE, Connor DF, Hampton KD, Richard NE, Modell JG. Bupropion XL in adults with attention-deficit/hyperactivity disorder: a randomized, placebo-controlled study. Biological Psychiatry, 2005 Apr 1; 57(7):793-801.
18 Swanson J, Greenhill L, Wigal T, Kollins S, Stehli A, Davies M, Chuang S, Vitiello B, Skroballa A, Posner K, Abikoff H, Oatis M, McCracken J, McGough J, Riddle M, Ghouman J, Cunningham C, Wigal S. Stimulant-related reductions in growth rates in the PATS. Journal of the Academy of Child and Adolescent Psychiatry, 2006 Nov; 45(11):1304-1313.
19 Greenhill L, Kollins S, Abikoff H, McCracken J, Riddle M, Swanson J, McGough J, Wigal S, Wigal T, Vitiello B, Skroballa A, Posner K, Ghuman J, Cunningham C, Davies M, Chuang S, Cooper T. Efficacy and safety of immediate-release methylphenidate treatment for preschoolers with attention-deficit/hyperactivity disorder. Journal of the Academy of Child and Adolescent Psychiatry, 2006 Nov; 45(11):1284-1293.
20 Wigal T, Greenhill L, Chuang S, McGough J, Vitiello B, Skrobala A, Swanson J, Wigal S, Abikoff H, Kollins S, McCracken J, Riddle M, Posner K, Ghuman J, Davies M, Thorp B, Stehli A. Safety and tolerability of methylphenidate in preschool children with attention-deficit/hyperactivity disorder. Journal of the Academy of Child and Adolescent Psychiatry, 2006 Nov; 45(11):1294-1303.
21 McGough J, McCracken J, Swanson J, Riddle M, Greenhill L, Kollins S, Greenhill L, Abikoff H, Davies M, Chuang S, Wigal T, Wigal S, Posner K, Skroballa A, Kastelic E, Ghouman J, Cunningham C, Shigawa S, Moyzis R, Vitiello B. Pharmacogenetics of methylphenidate response in preschoolers with attention-deficit/hyperactivity disorder. Journal of the Academy of Child and Adolescent Psychiatry, 2006 Nov; 45(11):1314-1322.