Feel chest tightness when you walk or climb stairs? Isosorbide mononitrate (ISMN) is a nitrate medicine many doctors use to prevent angina — the chest pain caused by reduced blood flow to the heart. It relaxes blood vessels so the heart gets more oxygen and works less hard. This page gives plain, useful facts so you know what to expect and how to use ISMN safely.
ISMN converts to nitric oxide in the body, which widens veins and arteries. That lowers the pressure the heart pumps against and eases chest pain. You’ll usually notice relief from angina attacks and fewer episodes when taken correctly.
Common side effects you might see are headaches, flushing, lightheadedness, and sometimes a fast heartbeat. Headaches tend to be worst when you start the drug and often get better after a few days. If you feel dizzy, sit or lie down until it passes.
ISMN comes in immediate-release and extended-release forms. Immediate-release doses are often given two or three times daily (for example, 10–20 mg). Extended-release tablets are usually taken once daily (often 30–60 mg). Your doctor will pick the right form and dose for you.
One important point: the body can get used to nitrates, reducing their benefit. Doctors commonly prescribe a nitrate-free interval (often overnight) so the medicine stays effective. Don’t skip that plan unless your doctor tells you otherwise.
Never mix ISMN with erectile dysfunction drugs like sildenafil (Viagra), tadalafil, or vardenafil. That combo can cause a dangerous drop in blood pressure. Also avoid strong blood pressure-lowering meds or large amounts of alcohol until you know how ISMN affects you. If you have very low blood pressure, severe anemia, or certain heart conditions (like hypertrophic cardiomyopathy), tell your doctor before using ISMN.
If you take other heart meds — beta blockers, calcium channel blockers, or ACE inhibitors — your doctor will check doses and watch for low blood pressure or worsening dizziness.
Missed a dose? Take it when you remember unless the next dose is close. Don’t double up. If you overdose or feel severe fainting, call emergency services right away.
ISMN is a prescription drug. Buy it from verified pharmacies only. Ask your pharmacist about proper storage (usually room temperature away from moisture) and check expiry dates. If you’re ordering online, stick to reputable sites and keep a printed or digital copy of your prescription.
If angina symptoms change — more frequent pain, pain at rest, or pain not relieved by your usual medication — contact your healthcare provider immediately. ISMN can prevent many angina attacks, but any new or worsening chest pain needs urgent attention.
Questions about dosing, timing, or interactions? Bring them up with your prescriber. A short talk can prevent side effects and make the medicine work better for you.
