Patients should consult their physician before taking any other medication (either prescription or over-the-counter) or nutritional supplements. Of particular concern to patients taking cholesterol drugs are other cholesterol medications. Taking more than one cholesterol reducer at a time may worsen side effects, unless a physician has prescribed a specially dosed combination of medications.

It is also important to consider the effects of over-the-counter and "herbal" remedies that purport to lower cholesterol. Because these preparations do not make explicit health claims, they do not undergo the same level of scrutiny by the U.S. Food and Drug Administration (FDA) as do prescription drugs. For example, the herbal substance guggul, derived from the mukul myrrh tree, has been advertised as a "cholesterol fighter." Researchers found, however, that it actually increased levels of LDL ("bad") cholesterol.

Other substances that may cause concern with some types of cholesterol-reducing drugs include:

• Birth control pills
  
  
• Immunosuppressives (drugs that suppress the body's immune system, used with organ transplants and autoimmune disorders such as rheumatoid arthritis)
  
  
• Inotropes (class of heart drugs)
  
  
• Anticoagulants
  
  
• Some antihypertensives (medications to treat high blood pressure) including diuretics, calcium channel blockers and certain beta blockers

• Azole antifungals (used for conditions such as yeast infections)
  
  
• Some antibiotics
  
  
• Certain nonsteroidal anti-inflammatory drugs (NSAIDs)
  
  
• Thyroid hormones
  
  
• Protease inhibitors (HIV drugs)

Patients taking cholesterol drugs may be instructed to avoid grapefruit juice. Grapefruit juice interferes with the liver's ability to rid the body of some substances. This could lead to a buildup of medications to toxic levels in the body. Though the buildup is less likely if the juice is ingested four or more hours prior to the medicine, patients taking cholesterol drugs are usually advised to refrain from drinking grapefruit juice. Patients may also be instructed to avoid eating grapefruit, tangelos and Seville oranges. Some research suggests that pomegranate juice may have similar effects on medications.