Attention-deficit/hyperactivity disorder (ADHD) is the most common behavioral disorder of childhood and is recognized as one of the most prevalent chronic health conditions in school-aged children, affecting an estimated 3% to 5% [1, 2]. The key features of ADHD include hyperactivity, impulsiveness, and inattention [1, 2]. Although its etiology remains unknown, data from family genetic, twin and adoption studies as well as segregation analysis suggest a genetic origin for some forms of this disorder [1, 2]. Successful management of ADHD relies heavily on the accuracy of its diagnosis, as well as on individualized treatment planning. According to guidelines, significant diagnostic components include 1) using DSM IV criteria  2) collecting information about the child's symptoms in more than one setting; and 3) looking for coexisting conditions that may impede the diagnostic process or complicate treatment planning [1, 2]. Stimulants are the most commonly used drug therapy in ADHD patients are burdened with a less than favorable pharmacokinetic and pharmacodynamic profile associated with their use [4–7]. In spite of the good response of many patients with ADHD to stimulant drugs, a substantial percent do not respond to or develop significant side effects from stimulants [8, 9]. For this reason, new investigations have been initiated for ADHD treatment [10, 11]. Deficiencies in certain vitamins and mineral have also been found to have some correlation with ADHD [12–14].
Zinc is an essential cofactor over 100 enzymes, both metalloenzymes and metal-enzyme complexes, required in the metabolism of carbohydrates, fatty acids, proteins, and nucleic acids [12, 13]. Past studies have suggested that there may be a correlation of zinc deficiency and pathophysiology of ADHD [12–14]. Melatonin is a hormone that plays an important role in the regulation of dopamine, thought to be a factor in ADHD . Melatonin is sold over the counter as dietary supplement and has been proven helpful in regulating the sleep cycle of children with ADHD. Zinc is involved in the production and modulation of melatonin, and therefore is also considered to be a factor in ADHD [12–14]. In this 6-week double blind, placebo controlled-trial, we assessed the effects of zinc plus methylphenidate vs. methylphenidate plus placebo in the treatment of children with attention deficit hyperactivity disorder. To our knowledge, this study is the first double blind and placebo controlled clinical trial assessing the adjunctive role of zinc in the ADHD.