Clonidine treatment of Gilles de la Tourette's syndrome. The safety and effectiveness of clonidine hydrochloride (3 to 5 micrograms/kg per day) were evaluated in 47 subjects with Gilles de la Tourette's syndrome, aged 7 to 48 years. Twenty-four subjects were randomly assigned to clonidine treatment and 23 to placebo. Forty subjects (21 given clonidine and 19 placebo) successfully completed the 12-week, double-blind clinical trial. Clinical ratings of tic severity improved for both groups. The magnitude of response was greater in the group receiving clonidine. Clinician-rated measures of motor tic severity, the degree to which the tics are "noticeable to others," motor tic counts from videotaped interviews, and parent-rated measures of impulsivity and hyperactivity were the most responsive to clonidine treatment. These results indicate that clonidine is more effective than placebo in reducing some of the tic and other behavioral symptoms associated with Gilles de la Tourette's syndrome. 