Imdur (Isosorbide Mononitrate): Uses, Dosage, Side Effects, and Safety Guide

Aug, 27 2025

If your doctor mentioned Imdur, you likely want clear answers now: what it does, how to take it without feeling lousy, what to avoid, and how to find the official label fast. I wrote this to give you the exact, practical stuff you’d ask in a clinic visit-without the fluff. I’m a dad in Seattle who cares about plain-English health info; I’ve seen how small medication misunderstandings can snowball into big problems. My goal is simple: help you use this drug safely and confidently.

What you’ll get here: a quick summary, the right way to take Imdur (with pro tips that actually help), what to expect (headaches are common at first), which meds never to mix with it, and a 60-second path to the official FDA label-because nothing beats primary sources when it’s your heart on the line.

• Know what Imdur is used for and what it isn’t (not for sudden chest pain).
• Get a safe dosing game plan and what to do if you miss a dose.
• Spot side effects you can ride out vs ones that mean “call now.”
• Avoid dangerous interactions (the PDE-5 inhibitor warning matters a lot).
• Navigate to the FDA label and medication guide in under a minute.

• TL;DR: Imdur is an extended-release nitrate (isosorbide mononitrate) to prevent angina; it won’t stop a current chest pain episode.
• Typical start: 30-60 mg once each morning; do not crush or chew. Your prescriber will tailor the dose.
• Headache, flushing, and dizziness are common early on-usually improve in a few days. Stand up slowly and hydrate.
• Never combine with sildenafil, tadalafil, vardenafil, or avanafil, or with riociguat-can cause severe, even fatal, blood pressure drops.
• For the official instructions (FDA label), go to the FDA’s Drugs@FDA or DailyMed and search “Imdur label.” Steps below.

What Imdur Is, How It Works, and Who It’s For

Imdur is the brand name for isosorbide mononitrate extended-release, a nitrate used to prevent angina (chest pain) in people with coronary artery disease. It’s meant to lower how hard your heart has to work by relaxing blood vessels (mostly veins), which reduces the amount of blood returning to the heart. Less pressure and less demand equals fewer angina episodes. Think of it as daily prevention, not an emergency fix.

Important distinction: Imdur won’t stop sudden chest pain. For that, doctors usually prescribe a short-acting nitrate like nitroglycerin tablets or spray to use at the moment symptoms start. If you’re not sure what you have for emergencies, ask your prescriber or pharmacist today.

How it works in plain terms: your body converts the drug into nitric oxide, which triggers cGMP in blood vessel muscle. That relaxes the vessel walls. The extended-release design spreads the effect out through the day and helps limit “tolerance” (your body getting used to the drug so it works less). Even so, tolerance can still happen if dosing is off-more on avoiding that in the dosing section.

Who typically gets it: people with chronic stable angina; sometimes it’s used along with beta-blockers, calcium channel blockers, or statins as part of a bigger heart plan. It can also be used when other angina meds aren’t enough or can’t be taken.

Who might not be a good fit: anyone taking PDE-5 inhibitors for erectile dysfunction (sildenafil, tadalafil, vardenafil, avanafil) or riociguat (for pulmonary hypertension)-these combos are flat-out contraindicated due to dangerous blood pressure drops. Also, people with severe low blood pressure, recent right-ventricular heart attack, or a history of serious nitrate reactions need a tight conversation with their cardiologist. If you’ve got orthostatic hypotension (you get dizzy on standing), you’ll need extra caution and slow dose changes.

Availability note: In the US, pharmacies mostly stock generic isosorbide mononitrate ER. Same active medication, just different makers. If your prescription literally says “Imdur” and they hand you a generic, that’s normal unless your doctor wrote “dispense as written.”

Quick personal aside: When my wife Faith and I plan morning schedules around Brantley’s school drop-off, I remind anyone in my family on heart meds: take them at the same time daily and don’t improvise the dose. Consistency protects you.

How to Take Imdur Safely: Dosing, Timing, and Missed Dose Rules

Most people start at 30-60 mg once daily in the morning. Some are titrated up to 120 mg or even 240 mg once daily depending on symptoms and tolerance, guided by a prescriber. Stay with the plan your clinician set for you-that’s what matches your history, your other meds, and your blood pressure.

Key rules that prevent problems:

• Do not crush or chew extended-release tablets. That can dump the dose too fast and drop your blood pressure.
• Only split the tablet if your specific product is scored and your prescriber or pharmacist says it’s okay. Many ER tablets shouldn’t be split.
• Take it at the same time each morning. Morning dosing gives a predictable effect and helps limit tolerance.
• With or without food is usually fine; if you get queasy, try a small breakfast with it.
• Avoid alcohol or keep it minimal-alcohol can amplify dizziness and low blood pressure.

About tolerance: Your body can adapt to nitrates if blood levels stay too high for too long. The once-daily extended-release schedule is designed to reduce that risk by creating lower levels later in the day. If your angina seems to creep back after weeks, don’t raise your dose on your own-message your prescriber. Sometimes the fix is a small timing tweak, not a bigger dose.

Missed dose playbook:

• If it’s been just a few hours, take it when you remember.
• If it’s late and close to your next dose, skip the missed one. Don’t double up.
• If you’re missing doses often, set a daily alarm or pair the pill with a morning habit (coffee, brushing teeth, dog walk).

When starting or increasing the dose, expect some headaches, flushing, or lightheadedness. This usually eases in a few days. Headaches can be surprisingly strong at first-counterintuitive, but it’s a sign the drug’s working on your blood vessels. Ask your doctor if you can use acetaminophen for a few days while your body adjusts; avoid NSAIDs (like ibuprofen) unless your clinician okays it for your heart history.

Driving and standing: Especially in week one, stand up slowly. If you feel woozy, sit or lie down and elevate your legs for a minute. Don’t drive or climb ladders right after taking the dose until you know how you respond.

Storage: Keep tablets dry at room temperature, and away from bathrooms and car glove boxes. Moisture and heat can degrade meds faster than you think.

Note: Numbers above reflect typical pharmacology data from the US prescribing information and drug monographs. Your response can differ based on age, other meds, kidney/liver function, and genetics.

Side Effects, Interactions, and When to Get Help

Common side effects (often improve after a few days):

• Headache or pressure across the forehead
• Facial flushing or warmth
• Dizziness or lightheadedness, especially on standing
• Nausea, fatigue

What helps: drink water, rise slowly, and time doses so the peak effect doesn’t hit during heavy activity. A short course of acetaminophen can help headaches if your clinician approves. If headaches are relentless after a week, or you’re missing life because of them, ask about dose adjustments-it’s a common fix.

Less common but important:

• Fainting or near-fainting
• Fast heartbeat (your body may reflexively speed up the heart when blood pressure dips)
• Severe or worsening chest pain (could mean under-treatment, tolerance, or a new heart issue)

Call your prescriber promptly if you notice these. If chest pain is new, intense, or not relieved by your rescue nitro, call emergency services.

Major interaction alerts (these are hard no’s):

• PDE-5 inhibitors: sildenafil (Viagra), tadalafil (Cialis), vardenafil (Levitra/Staxyn), avanafil (Stendra). Timing matters: avoid Imdur within 24 hours of sildenafil/vardenafil and within 48 hours of tadalafil. Your prescriber may advise a longer buffer depending on your case.
• Riociguat (Adempas): combining with nitrates can cause severe hypotension.

High caution with:

• Other blood pressure meds (beta-blockers, calcium channel blockers, ACE inhibitors/ARBs, diuretics): effects can stack. Not a dealbreaker, but monitor for dizziness.
• Alcohol: magnifies low blood pressure and fainting risk.
• Heat exposure, saunas, hot tubs: can drop blood pressure further when starting or titrating the dose.

Pregnancy and breastfeeding: Data are limited. Guidelines and labeling say weigh benefits and risks; for chronic angina in pregnancy, cardiology input is a must. If you’re pregnant, trying, or nursing, ask your cardiologist and OB to coordinate; they’ll weigh your specific risks and safer alternatives.

Allergy or intolerance: True nitrate allergy is rare. More often, people confuse the predictable early headaches with “allergy.” If you notice hives, swelling, or trouble breathing after a dose, that’s different-seek urgent care.

What if you accidentally take too much? Expect a pounding headache, flushing, nausea, and possibly fainting. Sit or lie down with legs raised. If you passed out, have chest pain, or feel severely ill, call emergency services. Bring the pill bottle so clinicians can see the exact drug and dose.

Evidence and sources: Everything here aligns with the US FDA prescribing information for isosorbide mononitrate (Imdur), the DailyMed monograph, and the 2023 American Heart Association/American College of Cardiology guideline for chronic coronary disease. Those are the gold standards your clinicians follow.

FAQs, Quick Checks, and How to Reach the Official Label Fast

If you came here wanting the shortest path to the official documents, this is your section. Two reliable destinations in the US: the FDA’s Drugs@FDA and DailyMed (the National Library of Medicine’s label repository). Here’s how to get there and what to click once you arrive.

1. On your phone or computer, open your search engine and type: FDA Drugs at FDA Imdur label
2. Open the Drugs@FDA result. In the drug record, look for “Label” or “Prescribing Information (PDF).” Tap that to view the full physician label and the “Patient Information/Medication Guide.”
3. For DailyMed, search: DailyMed Imdur isosorbide mononitrate. Open the matching record. Tap “Medication Guide” for the patient-friendly sheet and “Full Prescribing Information” for the clinician label.
4. Check the “Revision date” on the label. You want the most recent update.
5. Save the PDF for quick reference; it’s handy when you message your doctor or pharmacist.

How to scan the label fast (what matters most for you):

• Indications/Usage: Confirms it’s for angina prophylaxis and not acute relief.
• Dosage/Administration: Shows starting dose and how to titrate.
• Contraindications: The PDE-5/riociguat warnings live here.
• Warnings/Precautions: Headaches, hypotension, and tolerance notes.
• Drug Interactions: Cross-check with your current med list.

Mini-FAQ

• Does Imdur help during a chest pain attack? No. It’s for prevention. Use your short-acting nitroglycerin for symptoms, exactly as prescribed.
• How long until it helps? Some people notice fewer angina episodes in the first week; full effect may take longer as your dose is fine-tuned.
• Why do I get a headache? Nitrates widen blood vessels in the head too. It often fades after a few days. Ask about a short course of acetaminophen if needed.
• Can I exercise? Yes, with your cardiologist’s plan. Many people can exercise better once angina is controlled. Warm up gradually and carry your rescue nitro if prescribed.
• Is the generic as good? Generics must meet FDA quality and bioequivalence standards. If a switch causes issues, tell your pharmacist; sometimes a different manufacturer’s ER matrix feels different for a subset of people.
• What if my pharmacy says it’s out? Ask if they can order another manufacturer or transfer the script. In 2025, supply hiccups happen; pharmacies usually have alternatives within a day or two.

Checklist: before your next dose change

• Have you had any near-fainting or falls? If yes, update your prescriber first.
• Any new meds since your last visit (especially ED meds or blood pressure pills)?
• Are headaches still severe after a week? That’s a flag to adjust the plan.
• Do you have rescue nitroglycerin on hand and know how to use it?
• Are you taking it at the same time daily? If not, set a morning alarm now.

Quick decision guide

• You forgot this morning’s dose and it’s lunchtime: Take it now.
• You forgot and it’s almost bedtime: Skip it; restart tomorrow morning.
• You took sildenafil this afternoon and tonight’s Imdur is due: Skip tonight’s dose and call your prescriber for guidance. Do not mix.
• Headache is crushing on day 2: Message your clinician about short-term acetaminophen and whether to pause or reduce while titrating.

Next steps and troubleshooting by scenario

• New prescription: Ask your pharmacist to write the exact generic name and manufacturer on the bottle. If you feel off after a refill, it’s easier to trace.
• Traveling: Pack extra doses in your carry-on. Time-zone shift? Keep it “morning local time” and aim for roughly 24 hours between doses.
• Blood pressure runs low: Track readings for a week (morning and early afternoon). Share the numbers; sometimes the solution is a small schedule tweak.
• Costs: Ask your pharmacist for the lowest-cost generic option they stock. In 2025, most plans cover isosorbide mononitrate ER cheaply, but prices vary by manufacturer.
• Other heart meds: Bring the full list to appointments-beta-blockers, calcium channel blockers, ACE/ARBs, diuretics, statins. Imdur often plays nice with them, but your combo needs a tailored plan.

Why you can trust this: The dosing ranges, contraindications, and side-effect profiles here match the US FDA Prescribing Information for isosorbide mononitrate ER (Imdur) and the 2023 AHA/ACC chronic coronary disease guideline. I keep this guide current with those sources, because that’s exactly what your cardiologist does when they choose and adjust therapy.

Last note from a guy who reads labels for fun so you don’t have to: it’s easy to underestimate “routine” heart meds. Set that morning alarm, keep a tiny headache plan ready for week one, and never, ever combine Imdur with ED meds. Those three steps prevent most of the drama I see people run into.