Generic name: Isosorbide mononitrate.

Other brand names: Ismo, Monoket.

Imdur is an anti-anginal agent. It works by relaxing muscles of the veins and arteries. 

Quick Facts About Imdur


Used to prevent angina pectoris — crushing chest pain; does not relieve already present angina attacks.

Imdur Dosage

Take exactly as prescribed — once per day in the morning. May take with or without food, swallowed whole with half a glass of liquid. Do not substitute brands unless specifically directed by your doctor. Do not abruptly discontinue use; consult doctor for gradual tapering off of medication. Do not change dose to relieve headache; headache stopping may be sign of Imdur losing its effectiveness.

  • Usual adult dose: 20 milligrams taken 2 times per day.
  • Usual child dose: not generally prescribed for children.
  • Missed dose: take as soon as possible, unless almost time for next dose. In that case, do not take missed dose; go back to regular schedule. Do not double doses.

Imdur Side Effects

Overdose symptoms:

air hunger, bloody diarrhea, coma, confusion, difficulty breathing, fainting, fever, nausea, palpitations, paralysis, pressure in the head, profuse sweating, seizures, skin that is cold and clammy or flushed, slow heartbeat, throbbing headache, vertigo, visual disturbances, vomiting. If you suspect an overdose, immediately seek medical attention.

More common side effects: dizziness, headache.

Less common or rare  Imdur side effects: abdominal pain, abnormal hair texture, abnormal heart sounds, abnormal or terrifying dreams, abnormal vision, acne, anemia, anxiety, back pain, bacterial infection, black stools, breast pain, bronchitis, confusion, constipation, coughing, decrease in sex drive, depression, diarrhea, difficult or labored breathing, difficulty concentrating, diminished sense of touch, drooping eyelid, dry mouth, earache, excessive amount of urine, fatigue, fever, fluid retention and swelling, flu-like symptoms, flushing, frozen shoulder, gas, general feeling of illness, heart attack, heart failure, heart murmur, hemorrhoids, high blood pressure, hot flashes, impotence, inability to fall sleep, increased mucus from the lungs, increased sweating, indigestion, inflamed eyes, inflammation of the tongue, inflammation of the vagina, intolerance of light, irregular heartbeat, itching, joint pain, kidney stones, leg ulcer, loose stools, low blood pressure, migraine, muscle and/or bone pain, muscle weakness, nasal or sinus inflammation, nausea, nervousness, palpitations, paralysis, perforated eardrum, pneumonia, purple or red skin spots, rapid heartbeat, rash, ringing in ears, severe pain in calf muscles during walking, sleepiness, slow heartbeat, sore throat, stomach ulcer with or without bleeding, stuffy nose, tingling or pins and needles, tremor, twisted neck, urinary tract infection, vomiting, weakness, wheezing, worsening of angina pectoris, yeast infection.


Inform your doctor before combining Imdur with:

calcium blockers such as Calan, Cardizem, and Procardia.

Alcohol may cause swift blood pressure decrease, possibly resulting in light-headedness. 

Special Cautions

If pregnant or planning to become pregnant, inform your doctor immediately. Not known if Imdur appears in breast milk.

No special precautions apply to seniors.

Not generally prescribed for children.

  • Be extremely cautious if you are driving or participating in other potentially hazardous activities.
  • Inform your doctor of any medical conditions before Imdur therapy.
  • Use with caution: may cause severe low blood pressure.
  • Should not take if allergic to this or other heart medications containing nitrates or nitrites, or if you have recently had a heart attack or congestive heart failure.
  • May aggravate angina caused by other heart conditions.

Note: provides accurate and independent information prescription pills, over-the-counter medicines and natural products. This material is provided for educational purposes only and is not intended for medical advice, diagnosis or treatment. If you have questions about  dosage, or Imdur side effects, please contact your healthcare provider.