You should not use this medicine if you have had an allergic reaction to guanethidine, if you have congestive heart failure, pheochromocytoma (a tumor on the adrenal gland), or if you use monoamine oxidase (MAO) inhibitors such as Parnate®, Marplan®, Nardil®, or Eldepryl®.
Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.
Avoid drinking alcohol while using guanethidine.
Tell your doctor if you are using digoxin (Lanoxin®), diet pills, decongestants (such as pseudoephedrine or phenylpropanolamine), ephedrine, Ritalin®, diuretics (water pills), birth control pills, or medicines to treat depression (such as amitriptyline or imipramine), mental problems (such as chlorpromazine), or nausea (such as Compazine®).
If you are pregnant or breastfeeding, talk to your doctor before using this medicine.
Talk with your doctor before using guanethidine if you have asthma, a stomach ulcer, kidney disease, or have had a heart attack.
Tell your doctor or dentist that you are using guanethidine before having any surgery.
This medicine may make you dizzy or drowsy, especially when you first start using it. Avoid driving or using machinery until you know how the medicine will affect you.
Dizziness may be worse when you stand up quickly after you have been sitting or lying down. Getting up slowly from a sitting or lying position may help decrease dizziness. If you start to feel faint or dizzy, sit or lie down.
Dizziness may be a problem in the morning when you first get up, in hot weather, if you exercise, or if you drink alcohol. Avoid standing or exercising for long periods.
Tell your doctor if you get a fever. Your doctor may need to change your dose of the medicine while you have the fever.