What Is Isosorbide? Uses, Dosage, and What You Need to Know in 2026

Isosorbide is a medication in the nitrate drug class used primarily to prevent chest pain (angina) in people with coronary artery disease. It comes in two main forms — isosorbide mononitrate and isosorbide dinitrate — and has been used in heart care since the 1960s. Despite being an older drug, it remains a cornerstone of angina management in 2026.

What Is Isosorbide Used For?

The primary FDA-approved use of isosorbide is prevention of angina pectoris (chest pain) due to coronary artery disease. It is a maintenance medication — meaning it's taken daily to prevent angina from occurring, not to stop an attack once it starts. For acute angina relief, sublingual nitroglycerin is used instead.

Other uses include:

• Heart failure (as BiDil): A fixed-dose combination of isosorbide dinitrate 20 mg and hydralazine 37.5 mg (brand name BiDil) is FDA-approved to treat heart failure in African American patients, improving survival and reducing hospitalizations.
• Off-label uses: Isosorbide dinitrate has been used off-label for esophageal spasm and as adjunctive therapy for portal hypertension (to reduce variceal bleeding risk), typically alongside non-selective beta-blockers.

Isosorbide Mononitrate vs. Isosorbide Dinitrate: What's the Difference?

Both forms are nitrates that work the same way, but they differ in how the body processes them:

• Isosorbide mononitrate (ISMN): The active form. Absorbed directly without liver metabolism. More predictable blood levels. Brand names: Imdur (ER), Monoket, ISMO (all discontinued; generics available).
• Isosorbide dinitrate (ISDN): Converted to ISMN in the liver. More variable bioavailability. Requires more frequent dosing. Brand names: Isordil, Dilatrate-SR (generics available).

Isosorbide Dosage Forms and Strengths

Isosorbide mononitrate is available as:

• 10 mg and 20 mg immediate-release tablets (taken twice daily)
• 30 mg, 60 mg, and 120 mg extended-release tablets (taken once daily)

Isosorbide dinitrate is available as:

• 5 mg, 10 mg, 20 mg, and 30 mg immediate-release tablets (taken 2–3 times daily)
• 40 mg extended-release capsules (Dilatrate-SR, taken twice daily at least 18 hours apart)

How to Take Isosorbide: Dosing Schedule

The most important rule with isosorbide is maintaining a daily nitrate-free interval to prevent tolerance:

• ISMN immediate-release: Take 20 mg twice daily with doses 7 hours apart (e.g., 8 AM and 3 PM). The long overnight gap provides the nitrate-free interval.
• ISMN extended-release: Take 30–120 mg once daily in the morning. Start at 30–60 mg; dose may be increased to 120 mg if needed.
• ISDN immediate-release: Take 5–40 mg 2–3 times daily with an adequate nitrate-free period.

Do not crush, chew, or break extended-release tablets. Swallow them whole.

Is Isosorbide a Controlled Substance?

No. Isosorbide mononitrate and isosorbide dinitrate are not controlled substances. They have no DEA schedule and no abuse potential. Prescriptions can be written with refills and transferred between pharmacies without any special restrictions.

Who Should Not Take Isosorbide?

Isosorbide is contraindicated in:

• Patients taking PDE5 inhibitors (sildenafil, tadalafil, vardenafil, avanafil) — risk of fatal hypotension
• Patients taking riociguat (Adempas)
• Patients with severe hypotension or hypovolemia (dehydration)
• Patients with hypertrophic obstructive cardiomyopathy (can worsen symptoms)
• Patients with known allergy to nitrates or isosorbide

Key Takeaways About Isosorbide

• Prevents angina — does not stop an attack that's already started
• Must be taken on a schedule that includes a nitrate-free interval each day
• Never combine with ED medications — this is a life-threatening interaction
• All brand names discontinued — only generic versions available in 2026
• Don't stop suddenly — always consult your doctor before changing your dose or stopping

If you're struggling to find isosorbide at your pharmacy, medfinder can help locate which pharmacies near you have your formulation in stock. Want to understand how this medication actually works in your body? Read our in-depth guide: How Does Isosorbide Work?.