Isosorbide mononitrate

What isosorbide mononitrate (isosorbide-5-mononitrate) is and how it works

Isosorbide mononitrate is a nitrate vasodilator used mainly to prevent angina (chest pain) attacks caused by coronary artery disease. It is not fast-acting enough to treat an angina attack that has already started. (1) (2)

This medicine carries one of the most important drug-interaction warnings in cardiovascular medicine: combining it with medicines for erectile dysfunction (sildenafil, tadalafil, vardenafil) or with riociguat (used for certain types of pulmonary hypertension) can cause a severe, potentially life-threatening drop in blood pressure. This combination is genuinely contraindicated -- not merely discouraged -- confirmed identically in substance by both US and UK regulator sources. A second key safety theme is that standard tablets must be taken on an asymmetric schedule (not simply evenly spaced) to build in a nitrate-free period each day, or the medicine's antianginal effect will wear off (tolerance).

Mechanism of action: how isosorbide mononitrate (isosorbide-5-mononitrate) works

Isosorbide mononitrate is metabolised to nitric oxide, which relaxes vascular smooth muscle, dilating veins (reducing cardiac preload) and, at higher doses, arteries (reducing afterload), reducing myocardial oxygen demand. Rapidly and almost completely absorbed orally (90-100% bioavailability), with a plasma half-life of about 4-5 hours. (6) (1)

What isosorbide mononitrate (isosorbide-5-mononitrate) is used for

Before taking isosorbide mononitrate (isosorbide-5-mononitrate)

Do not take / not appropriate for

• Do NOT take isosorbide mononitrate if you are taking sildenafil, tadalafil, vardenafil, or any other PDE5 inhibitor. Combining them can cause severe, potentially life-threatening low blood pressure, fainting, or reduced blood flow to the heart. (all countries) (1) (2)
• Do NOT take isosorbide mononitrate if you are taking riociguat (used for certain types of pulmonary hypertension) -- this combination can also cause severe low blood pressure. (all countries) (1) (2)
• Do not take if you have very low blood pressure, have had a recent heart attack with low filling pressures, cardiogenic shock, hypertrophic obstructive cardiomyopathy, constrictive pericarditis, cardiac tamponade, significant valve narrowing, raised pressure inside the skull, marked anaemia, closed-angle glaucoma, or severe volume depletion. (United Kingdom (extensive list; broadly applicable)) (2)

Tell your clinician about

• Any erectile-dysfunction medicine you take or are considering (sildenafil, tadalafil, vardenafil) -- this combination is contraindicated.
• If you take riociguat.
• Any history of low blood pressure, fainting, recent heart attack, heart failure, glaucoma, or significant anaemia.
• If you drink alcohol regularly, since alcohol can worsen the blood-pressure-lowering effect.
• If you are pregnant or breastfeeding, since safety has not been established.
• Any other blood-pressure-lowering medicines you take.

How to take isosorbide mononitrate (isosorbide-5-mononitrate)

• Take exactly as directed by your clinician or on your product's label -- the schedule differs meaningfully between standard tablets and extended-release tablets.
• Standard (non-extended-release) tablets: take asymmetrically (not evenly spaced through the day) -- for example, a common regimen is one dose in the morning and a second dose about 7 hours later -- to build in a nitrate-free period of several hours daily. Skipping this pattern and spacing doses evenly can cause the medicine to stop working as well over time (tolerance).
• Extended-release/modified-release tablets: typically taken once daily, usually in the morning -- these are specifically designed to produce a high-then-low blood level pattern across the day and night that avoids the need for a separate nitrate-free dosing step.
• Swallow tablets whole with enough liquid, unless your specific product's label says a modified-release tablet may be divided.
• Do not stop this medicine suddenly without medical advice -- dose and frequency should be reduced gradually if stopping.
• Never combine with sildenafil, tadalafil, vardenafil, or riociguat.

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6)

Missed dose

This dossier's sources did not describe a specific universal missed-dose rule for isosorbide mononitrate. Because the timing of doses matters for maintaining a nitrate-free interval and avoiding tolerance, follow your specific product's patient information leaflet or ask your pharmacist or clinician if you miss a dose -- do not simply double up without checking first.

Overdose

Overdose can cause severe low blood pressure, a very fast or slow heart rate, severe headache, dizziness, fainting, and in serious cases, methemoglobinemia (a blood disorder reducing oxygen delivery) or shock. If an overdose is suspected, call a doctor or poison control centre immediately, or seek emergency care. (1)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Serious warnings

Interactions

• Sildenafil, tadalafil, vardenafil (PDE5 inhibitors): contraindicated -- can cause severe, potentially life-threatening hypotension, syncope, or myocardial ischaemia. (1) (2)
• Riociguat: contraindicated -- can cause hypotension by the same mechanism. (1) (2)
• Alcohol and other vasodilators: additive blood-pressure-lowering effect. (1)
• Calcium channel blockers and other blood-pressure-lowering medicines: increased risk of orthostatic hypotension. (1) (2)

Pregnancy, breastfeeding, kidney/liver function, age

Monitoring

Before starting

• Confirm you are not taking, and do not plan to take, any PDE5 inhibitor or riociguat.
• Check blood pressure and confirm no contraindicated condition (very low blood pressure, recent heart attack with low filling pressures, cardiac tamponade, closed-angle glaucoma, etc.).

During treatment

• Watch for dizziness or fainting, especially when standing up or after the first dose.
• Follow the specific asymmetric dosing schedule to prevent tolerance.
• Seek urgent care for any severe dizziness or collapse, particularly if a PDE5 inhibitor or riociguat may have been taken.

Storage

Store at room temperature, away from moisture and light, as directed on the product label. Keep out of reach of children.

Frequently asked questions

References

1. Isosorbide Mononitrate Tablets -- full prescribing information (Actavis Pharma/Teva)DailyMed (U.S. National Library of Medicine) / FDA-approved prescribing information · United States · accessed 2026-07-31 · source 1
2. Isosorbide Mononitrate Tablets 20 mg -- SmPC (Dexcel-Pharma Ltd)electronic medicines compendium (emc), United Kingdom -- Summary of Product Characteristics · United Kingdom · accessed 2026-07-31 · source 2
3. MONICOR (mononitrate d'isosorbide) -- extended-release capsules 20/40/60 mg, Pierre Fabre MedicamentHaute Autorite de Sante (HAS) / ANSM, France -- national medicine reference · European Union (France) · accessed 2026-07-31 · source 3
4. IMDUR, APO-ISMN, and pms-ISMN (isosorbide-5-mononitrate extended-release tablets) -- Health Canada Product MonographsHealth Canada -- Product Monograph and Drug Product Database · Canada · accessed 2026-07-31 · source 4
5. IMDUR, MONODUR, and APO-ISOSORBIDE MONONITRATE -- ARTG entriesTherapeutic Goods Administration (TGA), Australia -- ARTG entries · Australia · accessed 2026-07-31 · source 5
6. ISMO 40 Retard, ISMO 20, and Duride -- Medsafe Data Sheets; Pharmac supply-issue noticeMedsafe (New Zealand Medicines and Medical Devices Safety Authority) and Pharmac · New Zealand · accessed 2026-07-31 · source 6

Brand names by country

Single-ingredient isosorbide mononitrate (isosorbide-5-mononitrate) names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries