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Tenex Side Effects

Generic name: guanfacine

Medically reviewed by Last updated on Oct 28, 2023.

Note: This document contains side effect information about guanfacine. Some dosage forms listed on this page may not apply to the brand name Tenex.

Applies to guanfacine: oral tablet, oral tablet extended release.

Serious side effects of Tenex

Along with its needed effects, guanfacine (the active ingredient contained in Tenex) 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

Less common

Incidence not known

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

Symptoms of overdose

Other side effects of Tenex

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

Less common

Incidence not known

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:

For Healthcare Professionals

Applies to guanfacine: oral tablet, oral tablet extended release.


The most common adverse reactions were dry mouth, somnolence, headache, fatigue, dizziness, abdominal pain, constipation, appetite decreased, and sedation.[Ref]


Very common (10% or more): Dry mouth (up to 54%), abdominal pain (up to 15%), constipation (up to 15%)

Common (1% to 10%): Vomiting, diarrhea, nausea, abdominal/stomach discomfort

Uncommon (0.1% to 1%): Dyspepsia[Ref]

Nervous system

Very common (10% or more): Somnolence (up to 40.6%), headache (up to 28%), dizziness (up to 16%), sedation (10.2%)

Common (1% to 10%): Lethargy, convulsion, dizziness postural, syncope

Rare (less than 0.1%): Hypersomnia

Postmarketing reports: Tremor, paresthesias, vertigo, taste alteration, hypertensive encephalopathy[Ref]


Very common (10% or more): Fatigue (up to 22%)

Common (1% to 10%): Asthenia

Uncommon (0.1% to 1%): Chest pain

Rare (less than 0.1%): Malaise[Ref]


Very common (10% or more): Appetite decreased (up to 15%)

Common (1% to 10%): Weight increased

Frequency not reported: Body mass index increased

Postmarketing reports: Edema


Common (1% to 10%): Insomnia, depression, anxiety, affect lability, middle insomnia, nightmare, irritability

Uncommon (0.1% to 1%): Agitation, hallucination

Postmarketing reports: Confusion[Ref]


Common (1% to 10%): Hypotension, bradycardia, orthostatic hypotension, tachycardia

Uncommon (0.1% to 1%): Pallor, atrioventricular block first degree, sinus arrhythmia, blood pressure increased, heart rate decreased

Rare (less than 0.1%): Hypertension

Frequency not reported: QTc prolongation

Postmarketing reports: Palpitations, rebound hypertension


Common (1% to 10%): Impotence, enuresis

Uncommon (0.1% to 1%): Pollakiuria

Frequency not reported: Urinary frequency increased

Postmarketing reports: Erectile dysfunction[Ref]


Common (1% to 10%): Rash, pruritus

Postmarketing reports: Alopecia, dermatitis, exfoliative dermatitis


Uncommon (0.1% to 1%): Asthma

Postmarketing reports: Dyspnea


Uncommon (0.1% to 1%): ALT increased


Uncommon (0.1% to 1%): Hypersensitivity


Postmarketing reports: Arthralgia, leg cramps, leg pain, myalgia


Postmarketing reports: Blurred vision


1. Product Information. Tenex (guanfacine). Wyeth-Ayerst Laboratories. 2001;PROD.

2. Cerner Multum, Inc. UK Summary of Product Characteristics.

3. Product Information. Intuniv (guanfacine). Shire US Inc. 2009.

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.