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Guanabenz Side Effects

Applies to guanabenz: compounding powder, oral tablet


In comparative studies the overall incidence of side effects associated with guanabenz was as high or higher than that seen with methyldopa or clonidine, but particularly troublesome effects, such as sodium retention, mental depression or sexual dysfunction, which have been associated with these drugs, have not been associated with guanabenz.[Ref]

Nervous system

The most common side effects involve the nervous system. Drowsiness is a complaint in up to 35% of patients, and, with dry mouth, is the main reason some patients discontinue therapy. Weakness or dizziness each occur in 6% and headache in 2% in patients.[Ref]


Gastrointestinal side effects include dry mouth in up to 37%, constipation in 2%, and nausea in 1% of patients.[Ref]


Postural hypotension may not have been observed, at least during initial therapy with guanabenz, due to peripheral vascular resistance and cardiac output remaining unchanged.[Ref]

Although usually asymptomatic, guanabenz can decrease heart rate. Other cardiovascular side effects are rare. Unlike some other alpha-2-adrenoreceptor agonists, guanabenz is only rarely associated with orthostatic hypotension. Rebound hypertension can be a significant problem that may be accompanied by nervousness, palpitations, diaphoresis, anxiety, insomnia, malaise, and abdominal cramps. It has been observed anywhere from 16 to 72 hours after discontinuation of therapy.[Ref]


Nasal congestion has been reported in less than 3% of patients.[Ref]


Dermatologic rashes have been reported in less than 3% of patients.[Ref]


Ocular side effects are limited to rare cases of blurry vision.[Ref]


There are no serious endocrinologic side effects associated with guanabenz. The drug does not appear to adversely affect the lipid profile. Some data indicate significant decreases in total and LDL cholesterol levels during guanabenz therapy.[Ref]


There are no known clinically significant renal side effects from guanabenz. Acutely (within the first day of therapy), guanabenz may cause a mild water diuresis. Unlike some alpha-2-adrenoreceptor agonists, guanabenz is not associated with sodium and water retention.[Ref]

Some data have shown significant increases in glomerular filtration rate, natriuresis, and free water clearance associated with the use of guanabenz during the first few hours of therapy. Use of guanabenz for one week or more, however, has not been associated with significant changes in renal function parameters.[Ref]

Medically reviewed by Last updated on Nov 19, 2020.

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.