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Discontinued Warning IconPlease Note: This Brand Name drug is no longer available in the US.
(Generic versions may still be available.)

Ismelin Patient Information including How Should I Take

What should I discuss with my healthcare provider before taking guanethidine (Ismelin)?

You cannot take guanethidine if you

  • have pheochromocytoma;
  • have congestive heart failure; or
  • are taking a monoamine oxidase inhibitor such as isocarboxazid (Marplan), phenelzine (Nardil), or tranylcypromine (Parnate).

Before taking this medication, tell your doctor if you

  • have peptic ulcer disease (stomach ulcers) or another stomach disease;
  • have gallstones,
  • have kidney disease;
  • have any type of heart disease;
  • have asthma;
  • have ulcerative colitis;
  • are suffering from depression (especially if you have suicidal thoughts); or
  • are receiving electroconvulsive shock therapy.

You may require a dosage adjustment or special monitoring during treatment if you have any of the conditions listed above.

Guanethidine is in the FDA pregnancy category C. This means that it is not known whether guanethidine will be harmful to an unborn baby. Do not take guanethidine without first talking to your doctor if you are pregnant or could become pregnant during treatment.

Guanethidine passes into breast milk and may be harmful to a nursing infant. Do not take guanethidine without first talking to your doctor if you are breast-feeding a baby.

How should I take guanethidine (Ismelin)?

Take guanethidine exactly as directed. If you do not understand these directions, ask your pharmacist, nurse, or doctor to explain them to you.

Take each dose with a full glass of water.

Take guanethidine with food or milk if it causes stomach upset.

It is important to take guanethidine regularly to get the most benefit.

Do not stop taking guanethidine suddenly without first talking to your doctor. This could cause severely high blood pressure, nervousness, and anxiety.

Your doctor may want you to have blood pressure monitoring or other medical evaluations during treatment with guanethidine to monitor progress and side effects.

Store this medication at room temperature away from moisture and heat.

Side Effects Centers

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.


Get tips on handling your hypertension.