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Guanfacine Side Effects

In Summary

Commonly reported side effects of guanfacine include: weakness, drowsiness, constipation, dizziness, fatigue, sedation, hypotension, decreased blood pressure, and xerostomia. Other side effects include: impotence, and nausea. See below for a comprehensive list of adverse effects.

For the Consumer

Applies to guanfacine: oral tablet, oral tablet extended release

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

Severity: Major

You should check with your doctor immediately if any of these side effects occur when taking guanfacine:

More common:
  • Blurred vision
  • confusion
  • dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
  • sweating
  • unusual tiredness or weakness
Less common:
  • Chest pain or discomfort
  • cough
  • difficulty with breathing
  • fast, slow, or irregular heartbeat
  • increased need to urinate
  • lightheadedness, dizziness, or fainting
  • mental depression
  • noisy breathing
  • passing urine more often
  • pounding heartbeat
  • tightness in the chest

If any of the following symptoms of overdose occur while taking guanfacine, get emergency help immediately:

Symptoms of overdose:
  • Dizziness (extreme) or faintness
  • unusual tiredness or weakness (severe)

Severity: Minor

Some of the side effects that can occur with guanfacine 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:
  • Constipation
  • dizziness
  • drowsiness
  • dryness of the mouth
  • headache
  • irritability
  • nausea
  • sleepiness or unusual drowsiness
  • unusual drowsiness, dullness, tiredness, weakness, or feeling of sluggishness
  • upper abdominal or stomach pain
  • vomiting
  • weight gain
Less common:
  • Acid or sour stomach
  • belching
  • decreased appetite
  • decreased sexual ability
  • dry, itching, or burning eyes
  • heartburn
  • indigestion
  • lack or loss of strength
  • paleness of the skin
  • stomach discomfort, upset, or pain
  • trouble with sleeping

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
  • increased salivation
  • nervousness or restlessness
  • shaking or trembling of the hands and fingers
  • stomach cramps
  • sweating

For Healthcare Professionals

Applies to guanfacine: oral tablet, oral tablet extended release


Guanfacine is generally well-tolerated. In a study of 580 hypertensive patients, only 7% withdrew due to adverse side effects. In addition, most side effects were mild, dose-related, and resolved over time.[Ref]

Nervous system

Nervous system side effects have included fatigue or a sedative effect and dizziness in 33% and 15% of patients, respectively. After one year of therapy, the incidence of these side effects falls to 6% and 1%, respectively. Headaches occur in less than 5% of patients. Nervous system side effects associated with the extended-release formulation have included somnolence (38%), fatigue (14%), headache (24%), lethargy (6%), dizziness (6%), and postural dizziness (less than 2%).[Ref]


Gastrointestinal side effects have included dry mouth in up to 60% of patients. Constipation has been associated with the use of this drug in 14% of patients. After one year of therapy the incidence of dry mouth and constipation averages 15% and 3%, respectively. Gastrointestinal side effects associated with the extended-release formulation have included dry mouth (4%), upper abdominal pain (10%), nausea (6%), and dyspepsia (less than 2%).[Ref]


Cardiovascular side effects have included orthostatic hypotension and palpitations, each of which is rare. There is limited, indirect (ECG) evidence of left ventricular hypertrophy resolution after guanfacine therapy. Cardiovascular side effects associated with the extended-release formulation have included hypotension/decreased blood pressure (6%), atrioventricular block (less than 2%), bradycardia (less than 2%), and sinus arrhythmia (less than 2%) .[Ref]


Genitourinary complaints in male patients are limited to impotence, which is associated with higher doses (daily doses of 3 mg or more).[Ref]


Metabolic side effects associated with the extended-release formulation have included decreased appetite (5%), and constipation (3%).[Ref]


Psychiatric side effects associated with the extended-release formulation have included irritability (6%)

Postmarketing reports: Hallucinations[Ref]


Respiratory side effects associated with the extended-release formulation have included asthma (less than 2%).[Ref]


1. "Multum Information Services, Inc. Expert Review Panel"

2. Philipp E "Guanfacine in the treatment of hypertension due to pre-eclamptic toxaemia in thirty women." Br J Clin Pharmacol 10 (1980): s137-40

3. "Product Information. Tenex (guanfacine)." Wyeth-Ayerst Laboratories, Philadelphia, PA.

4. Jerie P, Lasance A "Long-term efficacy and tolerance of the antihypertensive agent guanfacine." Int J Clin Pharmacol Ther Toxicol 22 (1984): 170-4

5. "Product Information. Intuniv (guanfacine)." Shire US Inc, Florence, KY.

6. Jerie P "Clinical experience with guanfacine in long-term treatment of hypertension." Br J Clin Pharmacol 10 (1980): s37-47

7. Oster JR, Epstein M "Use of centrally acting sympatholytic agents in the management of hypertension." Arch Intern Med 151 (1991): 1638-44

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

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