Medically Reviewed on 3/31/2023

Generic Name: guanabenz (discontinued)

Brand Name: Wytensin (discontinued)

Drug Class: Alpha-2 Adrenergic Agonists, Central Acting; Antihypertensives

What is guanabenz, and what is it used for?

Guanabenz is a medication used to treat high blood pressure (hypertension), either as a single agent or with a thiazide diuretic, a type of drug that reduces blood pressure by increasing urination. Guanabenz is classified as a centrally acting alpha-2 adrenergic agonist, a medication that reduces blood pressure by slowing the activity of the sympathetic nervous system.

Currently, both guanabenz generic drug and the brand Wytensin have been discontinued and are no longer available in the U.S. Guanabenz is used as a calming agent in horses.

The sympathetic nervous system is the part of the central nervous system that increases blood pressure, heart rate, respiratory rate and pupil size. Excessive blood pressure can weaken and damage the vascular walls, increasing the risk for diseases such as heart attack and stroke. Guanabenz stimulates alpha-2 adrenergic receptors, protein molecules on nerve cells (neurons) in the sympathetic nervous system. Alpha-2 receptors slow down the sympathetic nervous system, and consequently, lower blood pressure and heart rate. 


  • Do not use guanabenz in patients with hypersensitivity to any component of the formulation.
  • Guanabenz causes sedation and drowsiness in many patients. Exercise caution when using this medication with central nervous system (CNS) depressants such as benzodiazepines, phenothiazines and barbiturates, it can have additive effects.
  • Use guanabenz with caution in patients with vascular insufficiency including:
  • Guanabenz should be tapered gradually, abrupt discontinuation can cause rebound hypertension.
  • Plasma concentration of guanabenz was found to be higher in patients with alcohol-induced liver disease than in healthy persons. Use guanabenz with caution and monitor blood pressure in hypertensive patients with chronic liver function impairment.
  • Guanabenz’s half-life is prolonged and clearance is decreased in patients with impaired kidney function. Use guanabenz with caution and carefully monitor blood pressure in patients with hypertension and renal impairment.


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What are the side effects of guanabenz?

Common side effects of guanabenz include:

Call your doctor immediately if you experience any of the following symptoms or serious side effects while using this drug:

  • Serious heart symptoms include fast or pounding heartbeats, fluttering in your chest, shortness of breath, and sudden dizziness;
  • Severe headache, confusion, slurred speech, severe weakness, vomiting, loss of coordination, feeling unsteady;
  • Severe nervous system reaction with very stiff muscles, high fever, sweating, confusion, fast or uneven heartbeats, tremors, and feeling like you might pass out; or
  • Serious eye symptoms include blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights.

This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.

What are the dosages of guanabenz?


  • 4 mg
  • 8 mg



  • Initial dose: 4 mg orally every 12 hours initially; may increase the dose by 4-8 mg/day at 1-2 week intervals
  • The maintenance dose range is typically 4-16 mg orally every 12 hours
  • Not to exceed 32 mg orally every 12 hours


  • Adverse central nervous system (CNS) effects; may cause bradycardia and orthostatic hypotension; not recommended as routine treatment for hypertension (Beers criteria)
  • Not drug of choice in elderly because of CNS effects
  • 4 mg orally once daily, gradually increase every 1-2 weeks


  • Safety and efficacy not established


  • Guanabenz overdose can cause excessive contraction of the pupils (miosis), irritability, low blood pressure (hypotension), sleepiness (somnolence), slow heartbeat (bradycardia) and sluggishness.
  • Overdose may be treated with symptomatic and supportive care, including administration of activated charcoal and gastric lavage to eliminate undigested drug, intravenous medications and fluids, and monitoring of vital signs until the patient is stable.

What drugs interact with guanabenz?

Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.

  • Guanabenz has no listed severe or serious interactions with other drugs.
  • Moderate interactions of guanabenz include:
    • bretylium
  • Guanabenz has no listed mild interactions with other drugs.

The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.

It is important to always tell your doctor, pharmacist, or health care provider of all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or health care provider if you have any questions about the medication.

Pregnancy and breastfeeding

  • There are no adequate and well-controlled studies on the safety of guanabenz use in pregnant women, however, animal reproductive studies indicate it can cause fetal harm. Use guanabenz during pregnancy only if benefits outweigh potential fetal risks.
  • It is not known if guanabenz is present in breastmilk. Use with caution in nursing mothers because many drugs are excreted in breastmilk, and it is likely guanabenz also is excreted in breastmilk.

What else should I know about guanabenz?

  • Take guanabenz exactly as prescribed.
  • Do not abruptly discontinue guanabenz. It should be tapered in consultation with your physician.
  • Guanabenz can cause sedation and drowsiness and impair mental abilities required for hazardous tasks. Avoid engaging in activities such as driving and operating heavy machinery until the drug’s effects can be determined.
  • Avoid alcohol and other drugs that can depress the central nervous system while taking guanabenz, it can have additive effects.
  • Store guanabenz safely out of reach of children.
  • In case of overdose, seek immediate medical help or contact Poison Control.

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Guanabenz is a discontinued medication used to treat high blood pressure (hypertension), either as a single agent or with a thiazide diuretic, a type of drug that reduces blood pressure by increasing urination. Guanabenz is classified as a centrally acting alpha-2 adrenergic agonist, a medication that reduces blood pressure by slowing the activity of the sympathetic nervous system. Guanabenz is used as a calming agent in horses. Common side effects of guanabenz include drowsiness, sedation, dry mouth (xerostomia), dizziness, weakness, headache, sleep disturbances, anxiety, depression, and impaired coordination, balance and speech (ataxia).

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You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

Medically Reviewed on 3/31/2023