Interactions

• Older people are vulnerable to drug interactions. They often take regular medications for chronic illness that make them more sensitive to other drugs. Diphenhydramine and other antihistamines can react with medications including tranquilizers, barbiturates and monoamine oxidase inhibitors. The drug interactions can cause fainting or a dangerously irregular heartbeat.
  
  

Sedation

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  The most common side effect is drowsiness, causing mild disorientation or dementia. An elderly person may fall asleep during normal activities. This sedating effect can cause unsteadiness. A person over 60 should get up slowly from a sitting or prone position to avoid fainting. If you take an anti-anxiety drug, it is not advisable to use diphenhydramine as the sedating effects exaggerate the effects of similar medications and may cause drug-related depression.
  
  

Prostate Complications

• Prostate problems such as an enlarged prostate or BPH affect many men over 60 years old. These prostate problems result in difficulties of urination or urine retention. It is important that the urine flow freely to take pressure off the enlarged prostate and urinary tract. Diphenhydramine and other antihistamines affect muscles in the prostate and bladder. This slows the flow of urine and complicates prostate problems.
  
  

Loss of Appetite

• Diphenhydramine is often used to calm motion sickness. Older people are more sensitive to its effects and may have nausea or lack of appetite. People who are frail or underweight may faint, have upset stomach or other digestive distress. If it is the only effective allergy medication for an older person, taking a smaller dose, taking it at bedtime, or taking the drug with food can minimize these side effects.
  
  

Warning

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  Read labels carefully regarding drug interactions with diphenhydramine or other antihistamines. Use the simple ingredient over-the-counter formula. Using combination drugs of diphenhydramine and pain relievers or decongestants can complicate an older person's drug regimen. If you or a relative is over 60 years old, consult a doctor before using diphenhydramine or other antihistamines.