Guanethidine (Oral)

Guanethidine is used to treat hypertension in children and adults.


Guanethidine is a prescription-only medicine indicated for the treatment of high blood pressure.

Hypertension, as this condition is otherwise known, increase the amount of energy and performance required by the heart and arteries. If the condition persists and is left untreated, patients become more susceptible to serious side effects of poorly managed high blood pressure. These include but aren't limited to:

  • Stroke
  • Heart Attack
  • Organ Failure

Medical studies indicate that when high blood pressure is consistently regulated with the aid of diet, exercise, stress management techniques, and prescription drugs like Guanethidine, these health conditions are less likely to occur.

Mechanisms of Action

Guanethidine targets specific nerve pathways with the goal of freeing and relaxing blood vessels so that the flow of blood is less restricted in hypertensive patients. Subsequently, this action helps to lower and control blood pressure.

Guanethidine used to be sold and marketed under the U.S. trade name Ismelin. Though this brand name is no longer available, other generics are offered on the marketplace today.

Conditions Treated?

  • Hypertension, High Blood Pressure

Type Of Medicine?

  • Antihypertensive

Side Effects

Common Side Effects of Guanethidine

Some of the most widely reported side effects of this medication include:

  • A frequent urge to go to the bathroom ' diarrhea
  • Abnormal heartbeat
  • Anxiety
  • Depression
  • Lethargy
  • Nasal congestion
  • Sexual dysfunction ' men only
  • Sudden weight gain
  • Swollen legs or feet ' edema
  • Syncope ' feeling faint or dizzy

These symptoms generally go away when patients become more acclimated to the treatment. If these side effects persist or become bothersome in day-to-day life, consult your healthcare professional.

Rare Side Effects of Guanethidine

In rare cases, Guanethidine may cause:

  • Blurriness
  • Dehydration
  • Difficulty breathing
  • Feeling nauseous
  • Frequent urination at night
  • Hair loss
  • A headache
  • Loose skin under eyelids
  • Pain in the chest
  • Pain in the muscles
  • Rashes on the skin


When it comes to administering medical treatments, no two patients are alike. Health care providers factor in several variables before personalizing treatment plans. When prescribing Guanethidine, for example, the following circumstances are evaluated before dispensing dosage amounts:

  • The medication strength
  • The timeline for treatment
  • The times per day required
  • The intervals between doses
  • Underlying medical problems
  • The patient's age and weight

This is stated to reiterate that doses should never be altered unless you have consulted with your healthcare provider. The following table outlines average amounts and does not substitute a prescription provided by your healthcare specialist:

Guanethidine Doses for Adults w/High Blood Pressure:

  • Initial Doses: 10 mg/12.5 mg | 1X Daily
  • Maintenance Doses: 25-50 mg | 1X Daily

Guanethidine Doses for Children w/High Blood Pressure:

  • Initial Doses: 200 mcg per Kg of Body Weight | 1X Daily
  • Maintenance Doses: May Increase Based on Tolerance Levels

Note: Increased dosage amounts should be completed slowly in gauged increments.

When Guanethidine Replaces Other Drugs

If Guanethidine is taking the place of another antihypertensive medicine, certain protocols must be exercised to reduce the risk of negative side effects. For example:

  • Replacing MAO Inhibitors' The transfer interval should be: 7 days of discontinuing the previous medicine before starting treatment with Guanethidine.
  • Replacing Ganglionic Blockers ' Patients should be slowly weaned off the previous medicine to prevent a sudden increase in blood pressure levels.

Guanethidine as an Adjunct Treatment

When Guanethidine is used in conjunction with other medications for controlling hypertension, extra care should be taken to prescribe the lowest dose amounts in order to reduce the chances of adverse side effects.

Missed Doses

If you forget to take your medication, take it as soon as you remember to do so. However, do not double the doses. If the next scheduled dose is drawing near, skip the missed dose and recommence the normal schedule.

To prevent missed doses, set an alarm for the same time every day or use an activity as a marker for when it's time to take it. Consider mealtimes, bathtime, and other common to-dos.


In the event of an overdose, call 911 immediately or the American Association of Poison Control Centers at 1-800-222-1222.


The following contraindications have been found for Guanethidine:

Drug Interactions

Negative interactions have been demonstrated when Guanethidine is used concurrently with the following drugs:

  • Pseudoephedrine
  • Doxepin
  • Moclobemide
  • Pargyline
  • Iproniazid
  • Toloxatone
  • Amitriptyline
  • Lazabemide
  • Nialamide
  • Amphetamine
  • Phenelzine
  • Yohimbine
  • Rasagiline
  • Clorgyline
  • Brofaromine
  • Iobenguane I 123
  • Furazolidone
  • Tranylcypromine
  • Selegiline
  • Isocarboxazid
  • Phenylpropanolamine
  • Phenylephrine
  • Procarbazine
  • Linezolid

Over the Counter Medicines

Study after study confirms that using popular OTC medicines concurrently with Guanethidine could raise blood pressure levels. Some examples of these OTCs include:

  • Weight loss and appetite control medicines
  • Medicines for asthma
  • Fever and cold medicines
  • Allergy drugs
  • Sinus treatments
  • Hay fever medications

As a result, do not take any OTC drugs before speaking with your healthcare specialist first.

Pre-Existing Medical Problems

Additionally, certain medical ailments may become worse with Guanethidine use. Extra care should be taken, therefore, when prescribing this antihypertensive drug in patients who are currently being treated for:

Kidney or liver disease, for instance, may delay the elimination of the medicine from the body. As a result, if this drug is prescribed, the following actions may be taken:

  • Close monitoring and frequent follow-ups
  • Adjusted doses if the medicine
  • Extra instructions for use


Pay attention to the warning label that comes with your medication. The following precautions are common:

Regulating High Blood Pressure

It is important to note that this antihypertensive medicine does not cure high blood pressure. It only helps to normalize blood pressure levels and consequently reduce the adverse effects of hypertension.

To maintain normal blood pressure levels, this medicine may be prescribed for life. However, this decision is based on individual patient assessments by a board-certified medical provider.

Discontinuing the Medicine

It is very important to continue to take this medicine as prescribed, even if you feel better.

Hypertension is often considered to be a silent disease because there are often no alarming symptoms.

A lot of patients are unaware of this condition until a checkup is performed at a healthcare provider. The absence of symptoms, however, does not take away the severity of the condition. As mentioned earlier, unchecked high blood pressure levels occurring for a prolonged period could lead to heart attack, stroke, organ failure, and increase patients' chances of developing dementia and vision issues over time.

Always consult your doctor before discontinuing Guanethidine or any other drug.

Lifestyle Changes

Most cases of hypertension are treated using a holistic approach. As an example, your doctor may advise you to complete additional steps to keep your blood pressure levels under control. The general guidelines include:

  • Subscribing to a low-sodium diet' high sodium levels are intricately linked to higher blood pressure readings.
  • Exercising every day ' patients who live an active vs. sedentary lifestyle generally fare better at follow-up visits.
  • Eating a well-balanced diet 'in addition to consciously choosing low-sodium foods, patients are advised to create meal plans that incorporate wholesome and nutritious foods. You may be referred to a dietician for help with eating a balanced diet.
  • Practicing stress management techniques' including deep breaths in tense situations or meditation to aid in reducing stress.


Before starting any new exercise or diet regime, consult your healthcare provider to verify this it is safe to do so.


This drug is noted for the side effect of fainting and dizziness, particularly when patients stand up suddenly after resting on a couch or bed. To reduce the risk of fainting or dizziness, your doctor may suggest getting up unhurriedly after sleeping or sitting down.

Syncope is mostly reported in the morning time after a night's rest. To alleviate this effect, an additional tip is to sit up slowly on one side of the bed and to let your feet hang off the edge for a few minutes before standing.

Other Triggers of Syncope

The following activities increase the risks of feeling lightheaded or dizzy when undergoing treatment with Guanethidine:

  • Drinking alcoholic beverages ' limit alcohol intake
  • Standing up all day 'decide to change positions during the workday, if possible
  • Rigorous exercise' consult your doctor before starting exercise activities
  • Overexposure to heat'“ dress appropriately for hot weather and take a bottle of water along to cool down


If you regularly feel faint or dizzy when using this medicine, consult your healthcare provider. An adjusted dose or alternative medicine may be required in this event.

Upcoming Medical Procedures

If you have a pre-planned surgery or dental procedure soon, tell your healthcare specialist that you are currently using Guanethidine, as this could affect how other medicines work, including anesthetics. Guanethidine, for example, could cause vascular collapse or cardiac arrest in patients who take it at the same time with an anesthetic drug. As a result, healthcare experts generally advise and confirm that patients have stopped using the medicine at least 14 days prior to surgery ' not excluding a dental procedure.

In the event of a medical emergency, healthcare specialists typically have protocols in place to address these risks.

Male Impotence

Male users may have trouble ejaculating during intercourse when using this medicine. This is caused by sympathetic blockade. However, this condition is reversible when the drug is discontinued. Tell your doctor if you are a male user who notices this side effect.


Before starting this treatment, tell your doctor if you have a history of allergies to any medicines, including antihypertensive treatments. Also, discuss with your healthcare provider any past adverse reactions to food, dyes, preservatives, or animal products.

Senior Patients

There are no limitations specified for prescribing Guanethidine in senior patients. However, it should be noted that seniors may be more vulnerable to the side effects of this drug. In particular, syncope has been reported in seniors using Guanethidine.

Expecting Mothers

It is unclear if this drug causes harm to fetuses or neonates. Unless completely necessary, this drug should not be given to pregnant or nursing mothers.

Medical Bracelet

As an extra measure of safety, it is suggested that patients using Guanethidine should always wear a medical bracelet. In the event of a medical emergency, EMTs get a quick overview of medications being taken and patients' medical history. Wearing a medical bracelet ultimately helps medical workers make an informed decision more quickly.


Keep this medication in the original container dispensed by your pharmacy and out of the reach of children.

Replace the cap and seal tightly after each use.

To preserve the quality of the medicine, store at room temperature and avoid:

  • Heat
  • Direct Light
  • Freezing Temperatures
  • Moisture

Pay attention to the expiration date listed on the prescription label. If the medicine is expired, consider returning to a local pharmacy where it can be discarded of in a safe manner.


Guanethidine, which is sold under the U.S. trade name Guanethidine, is suggested for the treatment of hypertensive patients. It is generally used as an adjunct treatment with dietary and lifestyle changes.

Medical researchers have confirmed that untreated hypertension, ranging from moderate to severe, could lead to serious and potentially fatal conditions, including heart attack, ischemia, and organ failure. Hypertension is moreover dubbed 'œa silent disease'due to the lack of notable symptoms. Fortunately, blood pressure checkups are routine at most doctors' visits and treatments such as Guanethidine oral tablets exist.

Taken once daily in most cases, the medicine works by relaxing the blood vessels and promoting better blood flow throughout the body. When the blood pressure levels are controlled, the heart and connecting arteries work less, reducing the risk of heart failure or a heart attack.

Guanethidine is a prescription-only medicine for children, adults, and seniors. Adjusted doses are based on patient's age, weight, and medical history. In general, a lower dose is provided at first to gauge patient responses and tolerance levels. If the preliminary doses are tolerated and work to lower blood pressure levels, the dose amount is usually increased.

Some patients end up taking Guanethidine for life. You should not stop using the medicine unless your doctor has told you to do so, even if you feel better. Additionally, read all warning labels associated with this drug to help keep you safe. For example, care should be taken when getting up after sitting or sleeping as fainting is a common side effect. Other triggers such as hot weather, exercise, or alcohol intake increase the chance of fainting.

Additionally, you should tell your doctor if you are taking any other medicines, including prescription and OTC drugs because negative interactions can occur. Healthcare experts generally suggest creating a full list of treatments and underlying conditions, including any history of allergies to determine if Guanethidine is safe to use.

To summarize, Guanethidine is effective at restoring high blood pressure to standard levels when patients use the drug as prescribed.