Duration of the hypotensive effect of guanfacine

Guanfacine given intravenously causes a brief rise in blood pressure. This is followed by a sustained decrease of blood pressure, accompanied in one case by a marked orthostatic effect. In addition to its lowering effect on blood pressure, guanfacine also reduces heart rate. The duration of action for up to 72 h is due to the long half-life of the drug. The main side effects observed are fatigue and sedation.