People with uncontrolled bleeding issues or a significantly low platelet count in their blood should avoid using Heparin. If they have ever been diagnosed with Heparin-induced thrombocytopenia (low platelet count produced by Heparin or pentosan polysulfate), they must not use Heparin. Those using NSAIDs or with heart infections, blood disorders, high blood pressure, etc., should inform their doctor before Heparin is administered.