Methylphenidate hydrochloride, also known as Ritalin, is the most commonly used central excitatory drug for the treatment of this disease, and is also the most commonly used drug for the treatment of this disease in China, with an effective rate of 75% to 80%. Benefits: A large number of clinical studies have shown that, within a short period of time, not only the core symptoms of ADHD (attention deficit, hyperactivity, impulsivity) are reduced, but also the related functions are improved, such as better discipline, less emotional activity, and better relationships with parents, teachers, and other children. The efficacy of MPH remains unclear. In addition, although central stimulants have been shown to improve behavior, many treated children do not fully recover normal behavior. In principle, central stimulants should not be used in preschool children; however, in individual children over 3 years of age with severe symptoms that are difficult to manage, some advocate their use as appropriate, but attention should be paid to their adverse effects. Disadvantages: Since MPH often takes a long time to treat this disease, various adverse reactions often occur. Common adverse reactions include: loss of appetite, nausea, abdominal pain, epigastric discomfort, vomiting, headache, dry mouth, insomnia, sluggishness, withdrawal behavior, emotional instability, agitation, crying, and increased heart rate and blood pressure. Of these, loss of appetite is often the biggest obstacle to medication use, making it impossible for many children to adhere. Children who take too high a dose or are overly sensitive to the medication may exhibit sluggishness. Some studies have also suggested that MPH inhibits height and weight gain in children during the 2 to 3 years of treatment for the disease, resulting in stunted growth; however, some studies have found no significant effect of MPH on height and weight in adolescents after 6 months to 6 years of follow-up. Also, the relationship between MPH use in adolescents and drug dependence in adulthood has been of interest.