Sounds like 'HEP-a-rin'

Heparin is an anticoagulant. It is used to treat and prevent blood clots, which can block your blood vessels. Find out how to use it safely and possible side effects.

What is heparin?

Heparin is known as an anticoagulant or 'blood thinner'. It is used to prevent blood clots from forming and existing clots from growing bigger. It works by interrupting the clot forming process and increasing the time it takes for blood clots to form.

Heparin is used to prevent blood clots after major surgeries such as hip or knee surgery, or abdominal surgery, and it is used if a blood clot has already formed such as in the heart (heart attack), leg (deep vein thrombosis) or lung (pulmonary embolism).      

Heparin is given by injection into a vein (intravenous) or under the skin (subcutaneous). 

Heparin is also used to prevent blood clots from forming in intravenous catheters. It is usually used when the catheter is first put in place, and every time that blood is drawn out of the catheter or medication is given through the catheter.


Tips for using heparin safely

Heparin is mostly used in hospital. If you are given heparin to inject yourself at home, your healthcare professional will teach you how to prepare and use it. Here are a few tips on how to use heparin safely:

  • Use the exact dose your doctor tells you to.
  • You will be shown where the injection can be given. Use a different place each time you give yourself an injection to stop skin from hardening. 
  • Call your doctor or nurse if you have redness, swelling, burning, or pain where you injected the heparin.
  • Use a new needle and syringe each time.
  • If you miss a dose contact your doctor right away. 
  • It is important to let health professionals know that you are taking heparin such as your dentist, your pharmacist, your podiatrist, your nurse. You may need to stop using this medicine for several days before having surgery, dental appointments or medical tests.
  • You will need to have regular blood tests and doctors visits while you are using heparin. 

Side effects

Like all medicines, heparin can causes side effects, but not everyone gets them. 

Side effects What should I do?
  • You will bleed easily
  • Use a soft toothbrush, waxed dental floss, electric razor; avoid sharp objects and fall risks (such as climbing a ladder)
  • Pain or bruising at the injection site 
  • Call your doctor if you have redness, swelling, burning, or pain where you injected the medicine
  • Signs of bleeding such as dark urine (wee), black stools (poo), bad headache, confusion, vision changes, dizziness, fainting, weakness or numbness
  • Tell your doctor immediately or ring HealthLine 0800 611 116
  • Signs of an allergic reaction such as skin rashes, itching, blisters, swelling of the face, lips, mouth or have problems breathing
  • Tell your doctor immediately or ring HealthLine 0800 611 116


Heparin should not be taken with some other medicines and herbal supplements. Tell your doctor or pharmacist about all medicines you are taking (including over the counter medicines), herbal and complementary medicines or recreational drugs. Your doctor or pharmacist will be able to check for any interactions. 

Learn more

The following links provide further information on heparin. Be aware that websites from other countries may contain information that differs from New Zealand recommendations.

Heparin Injection Medsafe Consumer Information (NZ)
Heparin (intravenous route, subcutaneous route) Mayo Clinic (US) 

Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 06 Nov 2016