Antihypertensive effect of guanfacine: a double-blind cross-over trial compared with clonidine.

1. Sixteen patients with essential hypertension were treated with guanfacine and with clonidine for 5 weeks each in a double-blind, placebo-controlled, cross-over trial. Dosage ranged from 2 to 6 mg guanfacine and from 0.3 to 0.9 mg clonidine daily in two or three divided doses. 2. Both compounds caused a significant and comparable decrease in blood pressure. Patients whose blood pressure was not reduced to normal by 2 to 3 mg guanfacine daily did not respond better to an increase in the dose. 3. Dryness of the mouth and constipation occurred with about equal frequency with both agents, but sedation and orthostatic circulatory effects were considerably more frequent with clonidine. 4. A withdrawal syndrome was observed on discontinuation of clonidine in one patient as opposed to no rebound hypertension on stopping guanfacine treatment. 5. Guanfacine caused a significant decrease in plasma noradrenaline and adrenaline, suggesting a decrease in sympatho-adrenal activity.