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Guanabenz Side Effects

For the Consumer

Applies to guanabenz: oral tablet

In addition to its needed effects, some unwanted effects may be caused by guanabenz. In the event that any of these side effects do occur, they may require medical attention.

Severity: Moderate

If any of the following side effects occur while taking guanabenz, check with your doctor or nurse as soon as possible:

Signs and symptoms of overdose
  • Dizziness (severe)
  • irritability
  • nervousness
  • pinpoint pupils
  • slow heartbeat
  • unusual tiredness or weakness

Minor Side Effects

Some of the side effects that can occur with guanabenz may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

More common:
  • Dizziness
  • drowsiness
  • dryness of mouth
  • weakness
Less common or rare:
  • Decreased sexual ability
  • headache
  • nausea

Side Effects: Post Treatment

After you stop taking this drug, it is possible that you may still experience side effects that need medical attention. If you notice any of the following side effects check with your doctor immediately:

  • Anxiety or tenseness
  • chest pain
  • fast or irregular heartbeat
  • headache
  • increased salivation
  • increase in sweating
  • nausea or vomiting
  • nervousness or restlessness
  • shaking or trembling of hands or fingers
  • stomach cramps
  • trouble in sleeping

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]


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]


1. "Product Information. Wytensin (guanabenz)." Wyeth-Ayerst Laboratories, Philadelphia, PA.

2. Hall AH, Smolinske SC, Kulig KW, Rumack BH "Guanabenz overdose." Ann Intern Med 102 (1985): 787-8

3. Rogers SJ "Guanabenz overdose." Ann Intern Med 104 (1986): 445

4. Nash DT "Clinical trial with guanabenz, a new antihypertensive agent." J Clin Pharmacol Oct (1973): 416-21

5. Walker BR, Deitch MW, Schneider BE, et al "Long-term therapy of hypertension with guanabenz." Clin Ther 4 (1981): 217-28

6. Leary WP, Asmal AC, Williams PC "Evaluation of the efficacy and safety of guanabenz versus clonidine." S Afr Med J 55 (1979): 83-5

7. McMahon FG, Ryan JR, Jain AK, et al "Guanabenz in essential hypertension." Clin Pharmacol Ther 21 (1977): 272-7

8. Dziedzic SW, Elijovich F, Felton K, et al "Effect of guanabenz on blood pressure responses to posture and exercise." Clin Pharmacol Ther 33 (1983): 151-5

9. Grenfell RF "Double-blind study of guanabenz acetate in hypertensive patients." South Med J 76 (1983): 199-201

10. Holmes B, Brogden RN, Heel RC, et al "Guanabenz: a review of its pharmacodynamic properties and therapeutic efficacy in hypertension." Drugs 26 (1983): 212-29

11. Baez MA, Woo-Ming RB, Garg DC, et al "Dose-ranging study to delineate the additive antihypertensive effect of guanabenz and captopril." J Clin Pharmacol 31 (1991): 312-7

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

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

14. 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 8 (1986): 973-7

15. Kaplan NM, Grundy S "Comparison of the effects of guanabenz and hydrochlorothiazide on plasma lipids." Clin Pharmacol Ther 44 (1988): 297-302

16. Venkata C, Ram S, Holland B, et al "Withdrawal syndrome following cessation of guanabenz therapy." J Clin Pharmacol Feb-Mar (1979): 148-50

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

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

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

20. Bauer JH "Effects of guanabenz therapy on renal function and body fluid composition." Arch Intern Med 143 (1983): 1163-7

21. Goldberg M, Gehr M, MacCarthy EP "Natriuretic and water diuretic effects of guanabenz: a central alpha-2 agonist." Trans Am Clin Climatol Assoc 95 (1983): 79-85

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

Not all side effects for guanabenz may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.