If you experience any of the following symptoms, consult your doctor right away: agitation, confusion, decreased urine output, depression, dizziness, headache, hostility, irritability, lethargy, muscle twitching, nausea, rapid weight gain, seizures, stupor, swelling of the face, ankles, or hands, or unusual tiredness or weakness. Some people develop a severe allergic reaction to ranolazine. If this happens, stop taking it and call your doctor immediately. Ranolazine reduces the activity of certain enzymes in your blood. It has been found to cause mild decreases in white blood cell counts, platelets, and hemoglobin levels. These changes are usually not a concern for most patients but could indicate an increased risk of bleeding if you take ranolazine with other medications that can also decrease these blood components. Do not take ranolazine if you have an active infection, such as a cold or the flu. Otherwise, there are no known interactions with anything else you might be taking. Ranolazine may not work for everyone. It has been used successfully to treat chronic pain but has not been approved by the FDA for this purpose. It has also been used unsuccessfully to treat acute pain (lasting less than one year) caused by heart attacks or strokes. So far, no studies have shown ranolazine to be harmful.