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

Heparin is one of the oldest and most widely used medications in modern medicine. First discovered in 1916, this injectable blood thinner has saved countless lives by preventing and treating dangerous blood clots. Whether you've been prescribed heparin or a loved one has been started on it during a hospitalization, this guide gives you the key facts you need in plain English.

What Is Heparin?

Heparin (generic name: heparin sodium) is an anticoagulant — a class of medications sometimes called blood thinners. Despite this nickname, heparin doesn't actually make your blood thinner. Instead, it reduces your blood's ability to form clots by blocking specific proteins (coagulation factors) in the clotting cascade. When clotting ability is reduced, harmful clots are less likely to form in blood vessels.

Heparin is derived from porcine (pig) intestinal mucosa and is given only by injection — it cannot be absorbed if taken by mouth. It is categorized as unfractionated heparin (UFH), distinguishing it from low-molecular-weight heparins like enoxaparin, which are related but different drugs.

What Is Heparin Used For?

Heparin is FDA-approved for a wide range of conditions and procedures:

Deep vein thrombosis (DVT): Treatment and prevention of blood clots in the deep veins of the legs, arms, or other areas

Pulmonary embolism (PE): Treatment and prevention of blood clots that travel to the lungs — a life-threatening emergency

Atrial fibrillation: Prevention of stroke-causing blood clots in patients with irregular heart rhythm

Cardiac and arterial surgery: Prevention of clot formation during open-heart surgery, bypass surgery, and other vascular procedures

Dialysis: Prevention of clot formation in the dialysis circuit during kidney dialysis sessions

DIC (disseminated intravascular coagulation): Treatment of a serious condition causing widespread, inappropriate clotting

Bridge therapy: Short-term injectable anticoagulation during transitions to or from oral blood thinners (e.g., warfarin)

Blood transfusions and lab procedures: Prevention of clotting in blood samples and transfusion lines

What Forms Does Heparin Come In?

Heparin comes only as an injectable solution. It is available in several concentrations and forms:

Single and multi-dose vials: 1,000 units/mL (10 mL, 30 mL); 5,000 units/mL (1 mL, 10 mL); 10,000 units/mL (1 mL); 20,000 units/mL (1 mL)

Carpuject syringes (Pfizer): Pre-filled syringe format at 5,000 units/mL and 10,000 units/mL

IV bags: 50 or 100 units/mL premixed with dextrose or saline, used for continuous IV infusions

Important: Always verify the concentration of your heparin vial before using it. Different concentrations look similar, and using the wrong strength can cause serious harm. Heparin carries a boxed warning about fatal overdoses from concentration errors.

How Is Heparin Dosed?

Heparin dosing varies widely by indication:

Prophylaxis (prevention of clots): Typically 5,000 units injected subcutaneously (under the skin) every 8-12 hours

Treatment of active DVT/PE: Initial IV bolus of 80 units/kg followed by continuous IV infusion at 18 units/kg/hr; adjusted based on aPTT results

Cardiac surgery: 300-400 units/kg IV bolus for procedures

Therapeutic IV heparin requires regular blood tests (aPTT — activated partial thromboplastin time) to ensure the dose is in the right range. Too little means clots may form; too much increases bleeding risk. This monitoring is one reason IV heparin is usually managed in a hospital or closely supervised outpatient setting.

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Is Heparin Available as a Generic?

Yes. Heparin sodium injection is available as a generic drug from multiple manufacturers including Pfizer, Hikma, Fresenius Kabi, Sagent, and Techdow USA. Because it is generic, it is generally lower in cost than brand-name alternatives. However, the ongoing shortage has made some formulations difficult to find even in generic form.

If you're having trouble finding heparin during the current shortage, medfinder can check which pharmacies near you have it in stock. And for a full overview of what to watch for while on this medication, see our guide on heparin side effects.