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Home / Drugs / Starting with G / Guanfacine

A centrally acting antihypertensive agent. The drug lowers both systolic and diastolic blood pressure by activating the central nervous system alpha-2 adrenoreceptors, which results in reduced sympathetic outflow leading to reduced vascular tone. Its adverse reactions include dry mouth, sedation, and constipation. [PubChem]
CategoriesAntihypertensive Agents
Adrenergic alpha-Agonists
ManufacturersShire development inc
Amneal pharmaceutical
Mikah pharma llc
Mylan pharmaceuticals inc
Watson laboratories inc
Promius pharma llc
PackagersActavis Group
Advanced Pharmaceutical Services Inc.
Amerisource Health Services Corp.
Amneal Pharmaceuticals
Atlantic Biologicals Corporation
Cardinal Health
Industriale Chimica S.R.L.
Major Pharmaceuticals
Murfreesboro Pharmaceutical Nursing Supply
Par Pharmaceuticals
Patheon Inc.
Pharmaceutical Utilization Management Program VA Inc.
Physicians Total Care Inc.
Promius Pharma
Resource Optimization and Innovation LLC
Shire Inc.
Southwood Pharmaceuticals
Watson Pharmaceuticals
SynonymsGuanfacina [INN-Spanish]
Guanfacine HCl
Guanfacine Hydrochloride
Guanfacinum [INN-Latin]
SPD 503


For use alone or in combination with other classes of antihypertensive agents in the management of hypertension. Has also been used for the treatment of attention deficit hyperactivity disorder (ADHD) in pediatric patients.


Guanfacine is a phenylacetyl-guanidine derivative hypotensive and a centrally-acting, alpha(2)-adrenergic receptor agonist used alone or in combination with other drugs for the treatment of hypertension.

mechanism of action

Guanfacine selectively stimulates central alpha(2)-adrenergic receptors, resulting in inhibition of sympathetic vasomotor centers, which contributes predominantly to the hypotensive effects of the drug. Central effects of guanfacine lead to reduced peripheral sympathetic nerve impulses from the vasomotor center to the heart and blood vessels. This results in a decrease in peripheral vascular resistance and a reduction in heart rate. The stimulation of peripheral alpha(2)-adrenergic receptors may also contribute to hypotensive effects.


Symptoms of overdose include drowsiness, lethargy, bradycardia and hypotension. LD50=165mg/kg (orally in mice)




Rapid and complete, with an oral bioavailability of approximately 80%.

half life

17 hours (range 10-30 hours)

route of elimination

In individuals with normal renal function, guanfacine and its metabolites are excreted primarily in the urine.

drug interactions

Treprostinil: Additive hypotensive effect. Monitor antihypertensive therapy during concomitant use.

Trimipramine: Trimipramine may reduce the antihypertensive effect of the alpha2-agonist, Guanfacine. Trimipramine may also increase the rebound hypertensive effect of Clonidine. Consider alternate therapy or monitor for changes in the therapeutic and adverse effects of Clonidine if Trimipramine is initiated, discontinued or dose changed. Guanfacine should be withdrawn very gradually to reduce the risk of hypertensive crisis.