Find & Manage Your Patient Assistance Programs
Estimated patient savings $600,000,000.00
Guanethidine sulfate oral

Important Note

The following information is intended to supplement, not substitute for, the expertise and judgment of your physician, pharmacist or other healthcare professional. It should not be construed to indicate that use of the drug is safe, appropriate, or effective for you. Consult your healthcare professional before using this drug.




WARNING: This medication can frequently cause dizziness and weakness which may lead to fainting, especially when first starting this medication. Symptoms occur more often upon awakening and may increase during hot weather, exercise, or when drinking alcohol. To avoid fainting do not stand quickly and avoid standing or exercising for long periods of time.


This medication relaxes and expands blood vessels and is used to treat high blood pressure (hypertension).

How To Use

Take this medication exactly as prescribed. Try to take it at the same time(s) each day. Take with food or milk to avoid stomach irritation. Do not stop taking this medication without consulting your doctor. Some conditions may become worse when the drug is suddenly stopped. Your dose may need to be gradually decreased. It is important to continue taking this medication even if you feel well. Most people with high blood pressure do not feel sick.

Side Effects

Dizziness, drowsiness, headache, diarrhea, sexual problems in males, loss of appetite, fatigue, and nasal congestion may occur as your body adjusts to the medication. Inform your doctor promptly if you develop: chest pain, shortness of breath, skin rash, swelling of the hands or feet, yellowing of the eyes or skin, severe diarrhea, fainting, muscle aches. If you notice other effects not listed above, contact your doctor or pharmacist.


Before taking guanethidine, tell your doctor if you have: heart or blood vessel disease, liver or kidney disease, stomach ulcers, diarrhea, asthma, fever, pheochromocytoma, diabetes. To avoid dizziness and lightheadedness when rising from a seated or lying position, change positions slowly. Avoid prolonged standing and be careful on stairs. Limit your intake of alcoholic beverages while taking this medication. Alcohol can lead to excessive drowsiness or fainting. Also avoid hot showers, saunas, or prolonged exercise as excessive heat can worsen dizziness. This medication should be used only when clearly needed during pregnancy. Discuss the risks and benefits with your doctor. It is not known if guanethidine passes into breast milk. Consult with your doctor before breast-feeding.

Drug Interactions

Before taking guanethidine, tell your doctor of all drugs you may use both prescription and nonprescription, especially: antidepressants, MAO inhibitors (e.g., furazolidone, linezolid, phenelzine, selegiline, tranylcypromine), drugs for mental conditions (e.g., phenothiazines, haloperidol, loxapine), diabetes medicines, drugs used for high blood pressure, weight loss drugs, birth control pills. Do not take any medication for coughs, colds or allergies without first checking with your doctor or pharmacist. Some of these products contain ingredients which can increase blood pressure. Do not start or stop any medicine without doctor or pharmacist approval.


If overdose is suspected, contact your local poison control center or emergency room immediately. Symptoms of overdose may include fainting or severe dizziness, unusually slow pulse, nausea, and vomiting.


It is important to have your blood pressure checked regularly while taking this medication. Learn how to monitor your blood pressure. Discuss this with your doctor. Do not allow anyone else to take this medication.

Missed Dose

If you miss a dose, take as soon as remembered; do not take if it is almost time for the next dose, instead, skip the missed dose and resume your usual dosing schedule. Do not "double-up" the dose to catch up.


Store at room temperature between 59 and 86 degrees F (between 15 and 30 degrees C) away from moisture and sunlight. Do not store in the bathroom.

Medical Alert

Your condition can cause complications in a medical emergency. For enrollment information call MedicAlert at 1-800-854-1166 (USA), or 1-800-668-1507 (Canada).