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Guanabenz Side Effects

Medically reviewed by Last updated on Feb 10, 2024.

Applies to guanabenz: compounding powder, oral tablet.


Do not stop taking this medication without first talking to your doctor. Stopping suddenly may make your condition worse.

This medication may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.

Avoid getting up too fast from a sitting or lying position, or you may feel dizzy. Get up slowly and steady yourself to prevent a fall.

Keep using this medicine as directed, even if you feel well. High blood pressure often has no symptoms. You may need to use blood pressure medication for the rest of your life.

Get emergency medical help if you have any of these signs of an allergic reaction while taking guanabenz: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have a serious side effect such as:

Less serious side effects of guanabenz may include:

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.

For Healthcare Professionals

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]


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]

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]


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]


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13. Olivari MT, Levine TB, Cohn JN. Acute hemodynamic and hormonal effects of central versus peripheral sympathetic inhibition in patients with congestive heart failure. J Cardiovasc Pharmacol. 1986;8:973-7.

14. Braden G, Alvis R, Walker BR, Cox M. Effects of guanabenz on sodium and water homeostasis. J Clin Hypertens. 1987;3:397-404.

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16. Dubrow A, Mittman N, DeCola P, et al. Safety and efficacy of guanabenz in hypertensive patients with moderate renal insufficiency. J Clin Hypertens. 1985;1:322-5.

17. Kaplan NM. Effects of guanabenz on plasma lipid levels in hypertensive patients. J Cardiovasc Pharmacol. 1984;6:s841-6.

18. Eldridge JC, Strandhoy J, Buckalew VM. Endocrinologic effects of antihypertensive therapy with guanabenz or hydrochlorothiazide. J Cardiovasc Pharmacol. 1984;6:s776-80.

19. Bosanac P, Dubb J, Walker B, et al. Renal effects of guanabenz: a new antihypertensive. J Clin Pharmacol. 1976;Nov-Dec:631-6.

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21. Bauer JH. Effects of guanabenz therapy on renal function and body fluid composition. Arch Intern Med. 1983;143:1163-7.

22. Gehr M, MacCarthy EP, Goldberg M. Guanabenz: a centrally acting, natriuretic antihypertensive drug. Kidney Int. 1986;29:1203-8.

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.