Patients should consult their physician before taking any other medication (either prescription or over-the-counter), nutritional supplements or herbal remedies. Substances that can intensify the effects of antihypertensives and possibly lead to low blood pressure (hypotension) include:

• Other antihypertensives (unless prescribed as part of a combination therapy).
  
  
• Nitrates. Medications that relax the arterial walls, causing a drop in blood pressure.
  
  
• Nicotinic acid. A form of vitamin B3 used as a cholesterol-reducing drug.
  
  
• Medications for sexual dysfunction.
  
  
• Alcohol.
  
  
• Grapefruit juice. Grapefruit juice interferes with the liver’s ability to rid the body of some substances. This could lead to a buildup of antihypertensives 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 antihypertensives are advised to refrain from drinking grapefruit juice. There is no indication that eating grapefruit (as opposed to drinking juice) presents any danger.

The following substances may counteract the effects of some antihypertensives and increase blood pressure.

• Narcotics (prescription painkillers).
  
  
• Nicotine (present in tobacco products such as cigarettes).
  
  
• Nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, Cox 2 inhibitors or ibuprofen.

In addition, some over-the-counter medications may adversely react with antihypertensives, including those for appetite control, asthma, colds, flu, cough, sinus problems or hay fever. People should also be careful of using eye drops for bloodshot eyes.