Evaluation of guanfacine and clonidine in essential hypertension: a single-blind crossover study.

The antihypertensive and side effects of guanfacine and clonidine were compared in 24 patients with essential hypertension in a single-blind crossover study. After four weeks of active treatment, both guanfacine and clonidine were equally effective in reducing blood pressure. After six weeks of active therapy, recumbent, but not standing, blood pressures were statistically higher (P < 0.01) when patients were taking guanfacine. Side effects were noted in all 24 patients, and resulted in the withdrawal of five patients (three of whom were receiving clonidine, one was receiving guanfacine and one was taking placebo). There were no significant changes in biochemical or haematological parameters during the trial. There was no evidence of "rebound" hypertension, but withdrawal symptoms did occur in one patient after therapy with guanfacine was discontinued.