You should not use Diltiazem if you are allergic to its components, or if you have:

• certain heart conditions, especially "sick sinus syndrome" or "AV block" (unless you have a pacemaker);
• low blood pressure; or
• if you have recently had a heart attack.

To make sure you can safely take diltiazem, tell your doctor if you have any of these other conditions:

• kidney disease;
• liver disease;
• congestive heart failure; or
• if you are also taking clonidine (Catapres).

FDA pregnancy category C. It is not known whether diltiazem will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant while using this medication. Diltiazem can pass into breast milk and may harm a nursing baby. Do not use diltiazem without telling your doctor if you are breast-feeding a baby.

Diltiazem may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert. Avoid drinking alcohol while taking diltiazem.

Grapefruit and grapefruit juice may interact with diltiazem and lead to potentially dangerous effects. Discuss the use of grapefruit products with your doctor.

Avoid exposure to sunlight or tanning beds. Diltiazem can make you sunburn more easily. Wear protective clothing and use sunscreen (SPF 30 or higher) when you are outdoors.

Get emergency medical help if you have any of these signs of an allergic reaction to diltiazem: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. Call your doctor at once if you have a serious side effect such as:

• a red, blistering skin rash;
• swelling in your hands or feet;
• trouble breathing;
• slow heartbeats;
• dizziness, fainting, fast or pounding heartbeat;
• upper stomach pain, itching, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes); or
• severe skin reaction -- fever, sore throat, swelling in your face or tongue, burning in your eyes, skin pain, followed by a red or purple skin rash that spreads (especially in the face or upper body) and causes blistering and peeling.

Less serious diltiazem side effects may include:

• headache;
• dizziness, weakness, tired feeling;
• upset stomach, nausea;
• sore throat, cough, stuffy nose; or
• flushing (warmth, redness, or tingly feeling).

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.