Patients should not take calcium channel blockers if they have been diagnosed with low blood pressure (hypotension). Calcium channel blockers may lower blood pressure to dangerous levels. In addition, patients should discuss with their physician the benefits and risks of taking calcium blockers if they have been diagnosed with any of the following conditions:

• Heart failure. The use of verapamil and diltiazem may slow cardiac conduction and reduce the contractile strength of the heart, potentially worsening heart failure. These drugs are generally contraindicated for patients with heart failure. This is not true for the long-acting dihydropyridines, which may be prescribed for patients with angina or high blood pressure in addition to heart failure.
  
  
• Heart attack (acute myocardial infarction). Large doses of fast-acting CCBs are linked to increased mortality and should therefore be avoided. However, certain calcium channel blockers may benefit some heart attack patients.
  
  
• Kidney or liver disease. These conditions may cause calcium channel blockers to be removed from the body at a slower rate, increasing the risk of overdose and/or side effects
  
  
• Abnormal heart rhythms (arrhythmias). Some types of calcium channel blockers may cause serious heart rhythm problems in patients with a history of arrhythmias (e.g., bradycardia, heart block).
  
  
• Clinical depression (or history of depression). Certain CCB (e.g., flunarizine) may cause depression in some patients.
  
  
• Parkinson’s disease (or similar disorders). A chronic progressive central nervous system disorder marked by tremors, a shuffling walk and weakness of resting muscles. Use of certain CCBs (e.g., flunarizine) may cause Parkinson-like symptoms in some patients.
  
  
• Other heart conditions. CCB use may worsen some other heart-related conditions.

Furthermore, preliminary studies suggested a link between calcium channel blocker use and an increased risk of breast cancer, particularly in postmenopausal women. Subsequent investigations found no substantial association between calcium channel blockers and breast cancer. Patients should discuss all the risks and benefits of this medication with their physicians.