The most common side effects associated with diltiazem are dizziness, headache, weakness, slow heartbeat, vomiting, diarrhea, constipation, nasal congestion, and a cough. Tell your doctor if any of these are severe or do not go away.
Rare, more serious adverse events have also been known to occur. Get immediate medical attention if you experience any new or worsening symptoms of heart failure (such as swelling of the feet/ ankles, shortness of breath, sudden weight gain, or unusual tiredness); mood changes; an abnormal heartbeat; severe abdominal pain; dark urine; yellowing eyes or skin; persistent vomiting; or any signs of an allergic reaction (such as rash; hives; itching; swelling of the face, tongue, or throat; or difficulty breathing or swallowing).
Talk to your doctor about your medical history - particularly if you have or have ever had a narrowing or blockage of your digestive system or any other condition that causes food to move through your digestive system more slowly; a heart attack; low blood pressure; or heart, liver, or kidney disease. Inform your doctor of all known allergies and of all medications, supplements, and herbal products that you take. Tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding.
This is not a complete list of side effects or precautions. For more information please visit the National Institutes of Health’s DailyMed webpage for diltiazem ER.