Hazardous agent. Causes bone marrow suppression, including potentially severe cytopenias. alpha-interferons may (rarely) cause aplastic anemia (use with caution in chronically immunosuppressed patients, with low peripheral blood counts or myelosuppression, including concurrent use of myelosuppressive therapy). Ulcerative or hemorrhagic/ischemic colitis observed with alpha-interferons. Acute hypersensitivity reactions and cutaneous reactions reported (rarely) with alpha-interferons. Hypertriglyceridemia reported. May cause or aggravate severe psychiatric adverse events (e.g. addiction relapse, depression, psychosis, mania, suicidal behavior/ideation) in patients with and without history of psychiatric disorder (use with extreme caution in history of psychiatric disorders, including depression). Higher doses may be associated with development of encephalopathy (higher risk in elderly patients). Ophthalmologic disorders (including decreased/loss of vision, macular edema, retinal hemorrhages, optic neuritis, papilledema, cotton wool spots, and retinal artery or vein thrombosis) occurred with peginterferon alpha-2b and/or with other alpha-interferons. Pancreatitis observed with alpha-interferon therapy. May cause or aggravate dyspnea, pulmonary infiltrates, pneumonia, bronchiolitis obliterans, interstitial pneumonitis, and sarcoidosis, which may result in respiratory failure. May cause or exacerbate autoimmune disorders (use with caution in autoimmune disorders). Use with caution in current or history of cardiovascular disease. Diabetes reported (use caution in history of diabetes mellitus, particularly if prone to DKA). Patients with chronic hepatitis C with cirrhosis, and patients coinfected with human immunodeficiency virus receiving highly-active antiretroviral therapy are at increased risk for hepatic decompensation. May cause or aggravate infectious disorders. May cause or aggravate ischemic disorders and hemorrhagic cerebrovascular events. Use with caution in renal impairment (CrCl <50 mL/minute), and in thyroid disorders (may cause or aggravate hyper- or hypothyroidism). Combination treatment with ribavirin may cause birth defects and/or fetal mortality; hemolytic anemia (may worsen cardiac disease), genotoxicity, mutagenicity, and may possibly be carcinogenic. Use with caution in the elderly. Combination therapy with ribavirin contraindicated in pregnancy.