Get emergency medical help if you have signs of an allergic reaction to heparin: nausea, vomiting, sweating, hives, itching, trouble breathing, swelling of your face, lips, tongue, or throat, or feeling like you might pass out.
Heparin may cause you to bleed more easily, which can be severe or life-threatening. You may also have bleeding on the inside of your body. Seek emergency medical attention if you have:
skin warmth or discoloration;
chest pain, irregular heartbeats;
shortness of breath, dizziness, anxiety, sweating;
any unusual bleeding or bruising;
severe pain or swelling in your stomach, lower back, or groin;
dark or blue-colored skin on your hands or feet;
nausea, vomiting, loss of appetite;
unusual tiredness;
any bleeding that will not stop; or
nosebleed, blood in your urine or stools, black or tarry stools, or coughing up blood or vomit that looks like coffee grounds.
Heparin can cause you to have bleeding episodes while you are using it and for several weeks after you stop.
Bleeding may be more likely in older adults, especially women over 60 years of age
Stop using this medicine and call your doctor at once if you have:
skin changes where the medicine was injected;
fever, chills, runny nose, or watery eyes;
easy bruising, unusual bleeding, purple or red spots under your skin; or
signs of a blood clot - sudden numbness or weakness, problems with vision or speech, swelling or redness in an arm or leg.
Common heparin side effects may include:
unusual bleeding or bruising;
uncontrolled bleeding;
allergic reactions; or
abnormal liver function tests.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Heparin side effects (more detail)
