The literature on the clinical use of clonidine for attention deficit hyperactivity disorder (ADHD), from 1980-1999, was reviewed at the Department of Psychiatry, University of Massachusetts Medical School, Worcester, MA. In 11 studies analyzed clonidine had positive effects in the treatment of ADHD and ADHD comorbid with conduct disorder, developmental delay, and tic disorder. The benefits were reported by clinician, parent, and teacher, and the effect was of moderate size (0.58 +/- 0.16) and less than that of stimulants. The effect was significantly greater for the ADHD-alone group. Clonidine was associated with a high prevalence of side effects, especially sedation, irritability, night awakening, hypotension, and dizziness. Two studies using the transdermal system reported a high percentage of localized rash, erythema, and skin irritation under the patch. In one of 3 studies with ECG data, changes were noted but no cardiac symptoms. 
COMMENT. Clonidine is a second line treatment for ADHD and is less effective than stimulants, even in patients with comorbid disorders. A moderate size benefit is associated with a high incidence of side effects. In combination with stimulants, the risk of serious side effects is a concern, and a treatment to be avoided pending further study. The disappointing results of this meta-analysis may promote a greater interest in Tenex as an alternative treatment for ADHD children with comorbidity, including tics, insomnia, and oppositional defiance disorder.