Heparin
Say it: HEP-uh-rin
Heparin is a blood thinner given as a drip or shot to prevent and treat harmful blood clots.
What it is
Heparin helps a natural protein in your blood block clotting. It works fast and wears off fast. This makes it useful in the hospital, where the dose can be changed quickly.
Often used for
- treating blood clots in the legs or lungs
- preventing clots in people in the hospital or after surgery
- preventing clots during heart surgery, dialysis, and some procedures
- some heart problems, like certain heart attacks
- keeping some ports and catheters from clogging, in small amounts
How you get it
It is usually given in the hospital as a steady drip into a vein, or as a shot under the skin. Small amounts may be used to flush a port or catheter. Your schedule may be different.
Common side effects and what helps
- Bruising more easily. Use a soft toothbrush and an electric razor.
- Small bleeding, like from your gums or nose. Press firmly for 10 minutes. Call if it does not stop.
- Heavier periods. Tell your team if your periods change.
- Bruising, pain, or redness where the shot goes in. Tell your nurse if it is getting worse.
- Mild allergic reactions like itching or chills. Tell your nurse right away.
Call your care team right away if you have
- Bleeding that will not stop, such as a nosebleed or a cut that keeps bleeding
- Red, pink, or dark brown urine
- Red or black stools that look like tar
- Coughing up blood, or throwing up blood or something that looks like coffee grounds
- A sudden bad headache, confusion, weakness, or trouble seeing or speaking
- Signs of an allergic reaction, like trouble breathing, swelling of the face or throat, or hives
- New pain, swelling, or coldness in an arm or leg, which can mean a new clot
Before you start, tell your team
- If you have ever had a low platelet count from heparin (heparin-induced thrombocytopenia)
- If you are allergic to heparin or pork products
- If you have ever had bleeding problems or stomach ulcers
- All medicines, vitamins, and herbs you take, especially aspirin and other blood thinners
- If you are pregnant or breastfeeding
Good to know
- Rarely, heparin causes a serious drop in platelets with new clots. You will have blood tests to check your platelet count.
- When given as a drip, you will have frequent blood tests to keep the dose in a safe range.
- Using heparin for a long time can weaken bones.
- Heparin comes in many strengths. Your care team will check the strength carefully each time.
At home
- If you flush a port or catheter at home, use only the syringes your team gave you and follow their steps.
- Check the label strength before each flush. Ask your team if anything looks different.
- Throw away used syringes the way your team showed you.
Questions to ask
- Why do I need heparin instead of a pill?
- How often will my blood be checked?
- Will I need a blood thinner after I leave the hospital?
Side effect guides
Sources
Quick answers
- What is Heparin?
- Heparin is a blood thinner given as a drip or shot to prevent and treat harmful blood clots.
- What is Heparin used for?
- treating blood clots in the legs or lungs; preventing clots in people in the hospital or after surgery; preventing clots during heart surgery, dialysis, and some procedures; some heart problems, like certain heart attacks; keeping some ports and catheters from clogging, in small amounts.
- How is Heparin given?
- It is usually given in the hospital as a steady drip into a vein, or as a shot under the skin. Small amounts may be used to flush a port or catheter. Your schedule may be different.
- What are the common side effects of Heparin?
- Bruising more easily. Small bleeding, like from your gums or nose. Heavier periods. Bruising, pain, or redness where the shot goes in. Mild allergic reactions like itching or chills.
- When should I call my care team while taking Heparin?
- Bleeding that will not stop, such as a nosebleed or a cut that keeps bleeding; Red, pink, or dark brown urine; Red or black stools that look like tar; Coughing up blood, or throwing up blood or something that looks like coffee grounds; A sudden bad headache, confusion, weakness, or trouble seeing or speaking; Signs of an allergic reaction, like trouble breathing, swelling of the face or throat, or hives; New pain, swelling, or coldness in an arm or leg, which can mean a new clot.
Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.