Skip to content
My WebMD Sign In, Sign Up

Phen oral

Guanethidine/Sympathomimetics (Indirect Acting)

This information is generalized and not intended as specific medical advice. Consult your healthcare professional before taking or discontinuing any drug or commencing any course of treatment.

Medical warning:

Serious. These medicines may interact and cause very harmful effects. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.

How the interaction occurs:

When these two medicines are taken together, your sympathomimetic may decrease the ability of guanethidine to lower your blood pressure.

What might happen:

Your blood pressure may increase.

What you should do about this interaction:

If your doctor prescribes these two medicines together, you may need to check your blood pressure more often. It may be necessary to change you to a different blood pressure medicine.Your healthcare professionals (e.g. doctor or pharmacist) may already be aware of this drug interaction and may be monitoring you for it. Do not stop, start, or change the dosage of any medicine before checking with them first.

References:

1.Day MD. Effect of sympathomimetic amines on the blocking action of guanethidine, bretylium and xylocholine. Br J Pharmacol 1962;18:421-39.
2.Day MD, Rand MJ. Antagonism of guanethidine by dexamphetamine and other related sympathomimetic amines. J Pharm Pharmacol 1962 Sep;14:541-9.
3.Gokhale SD, Gulati OD, Udwadia BP. Antagonism of the adrenergic neurone blocking action of guanethidine by certain antidepressant and antihistamine drugs. Arch Int Pharmacodyn Ther 1966 Apr;160(2):321-9.
4.Gulati OD, Dave BT, Gokhale SD, Shah KM. Antagonism of adrenergic neuron blockade in hypertensive subjects. Clin Pharmacol Ther 1966 Jul-Aug; 7(4):510-4.
5.Misage JR, McDonald RH Jr. Antagonism of hypotensive action of bethanidine by "common cold" remedy. Br Med J 1970 Nov 7;4(731):347.
6.Starke K. Interactions of guanethidine and indirect-acting sympathomimetic amines. Arch Int Pharmacodyn Ther 1972 Feb;195(2):309-14.
7.Ober KF, Wang RI. Drug interactions with guanethidine. Clin Pharmacol Ther 1973 Mar-Apr;14(2):190-5.

See 1 Reviews for this Drug. - OR -

Review this Treatment

Find a Drug:

by name or medical condition or shape/color (Pill Identifier)

(for example: aspirin)

(for example: diabetes)

Report Problems to the Food and Drug Administration
 
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.

Health Solutions From Our Sponsors

Ask the pharmacist

Questions about medications? Get expert answers by video or live chat about allergies, pregnancy, sleep, and more.
See the Ask the Pharmacist event schedule.

Ask a Question

Popular Slideshows & Tools on WebMD

tea
What you should eat.
Woman sitting in front of UV lights
Is yours working?
woman using breath spray
What's causing yours?
colon xray
Get the facts.
MS Overview
Recognizing symptoms.
bowl of yogurt with heart shape
Eat for a healthy heart.
woman doing pushups
To help you get fit.
Colored x-ray of tooth decay
Know what to look for.
Woman sitting with child
Do you know the symptoms?
fruit drinks
Foods that can help you focus.
Sad dog and guacamole
Don't feed this to your dog.
Thyroid exam
See how much you know.

Women's Health Newsletter

Find out what women really need.

WebMD the app

Get trusted health information. Whenever. Wherever... with your iPhone, iPad or Android.

Find Out More

IMPORTANT: About This Section and Other User-Generated Content on WebMD

The opinions expressed in WebMD User-generated content areas like communities, reviews, ratings, or blogs are solely those of the User, who may or may not have medical or scientific training. These opinions do not represent the opinions of WebMD. User-generated content areas are not reviewed by a WebMD physician or any member of the WebMD editorial staff for accuracy, balance, objectivity, or any other reason except for compliance with our Terms and Conditions. Some of these opinions may contain information about treatment or uses of drug products that have not been approved by the U.S. Food and Drug Administration. WebMD does not endorse any specific product, service, or treatment.

Do not consider WebMD User-generated content as medical advice. Never delay or disregard seeking professional medical advice from your doctor or other qualified healthcare provider because of something you have read on WebMD. You should always speak with your doctor before you start, stop, or change any prescribed part of your care plan or treatment. WebMD understands that reading individual, real-life experiences can be a helpful resource but it is never a substitute for professional medical advice, diagnosis, or treatment from a qualified health care provider. If you think you may have a medical emergency, call your doctor or dial 911 immediately.