Guanfacine Side Effects

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.

For the Consumer

Applies to guanfacine: oral tablet, oral tablet extended release

Along with its needed effects, guanfacine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while 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

Get emergency help immediately if any of the following symptoms of overdose occur while taking guanfacine:

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

Some side effects of guanfacine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

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

After you stop using this medicine, it may still produce some side effects that need attention. During this period of time, check with your doctor immediately if you notice the following side effects:

  • 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.

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%).


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%).


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%) .


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


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


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

Postmarketing reports: Hallucinations


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

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