A commonly used name is difenidol.

• Antiemetic
• antivertigo agent

Diphenidol (dye-FEN-i-dole) is used to relieve or prevent nausea, vomiting, and dizziness caused by certain medical problems.

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For diphenidol, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to diphenidol. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—Diphenidol has not been shown to cause birth defects or other problems in human or animal studies.

Breast-feeding—Diphenidol has not been reported to cause problems in nursing babies.

Children—There is no specific information comparing use of diphenidol for dizziness in children with use in other age groups. Also, there is no specific information about the use of diphenidol for nausea and vomiting in children who weigh less than 22.8 kilograms (50 pounds).

Older adults—Many medicines have not been studied specifically in older people. Therefore, it may not be known whether they work exactly the same way they do in younger adults or if they cause different side effects or problems in older people. There is no specific information comparing use of diphenidol in the elderly with use in other age groups.

Other medicines—Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking diphenidol, it is especially important that your health care professional know if you are taking any of the following:

• Central nervous system (CNS) depressants (medicines that cause drowsiness) or
• Tricyclic antidepressants (medicine for depression)—Using these medicines with diphenidol may increase the CNS depressant effects

• Enlarged prostate or
• Glaucoma or
• Intestinal blockage or
• Low blood pressure or
• Stomach ulcer—Diphenidol may make the condition worse

• Kidney disease or
• Urinary tract blockage—Higher blood levels of diphenidol may occur, increasing the chance of side effects

If you are taking diphenidol to prevent nausea and vomiting, it may be taken with food or a glass of water or milk to lessen stomach irritation, unless otherwise directed by your doctor. However, if you are already suffering from nausea and vomiting, it is best to keep the stomach empty, and this medicine should be taken only with a small amount of water.

Take this medicine only as directed. Do not take more of it and do not take it more often than directed by your doctor. To do so may increase the chance of side effects.

Dosing—

The dose of diphenidol will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of diphenidol. If your dose is different, do not change it unless your doctor tells you to do so.

The number of tablets that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are taking diphenidol.

• For oral dosage form (tablets):
  • Adults: 25 to 50 milligrams (mg) every four hours as needed.
  • Children: The dose is based on body weight and must be determined by the doctor.

Missed dose—

If your doctor has ordered you to take this medicine on a regular schedule and you miss a dose, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage—

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store the tablet form of this medicine in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

This medicine will add to the effects of alcohol and other CNS depressants (medicines that make you drowsy or less alert). Some examples of CNS depressants are antihistamines or medicine for hay fever, other allergies, or colds; sedatives, tranquilizers, or sleeping medicine; prescription pain medicine or narcotics; barbiturates; medicine for seizures; muscle relaxants; or anesthetics, including some dental anesthetics. Check with your doctor before taking any of the above while you are using this medicine.

This medicine may cause some people to have blurred vision or to become dizzy, drowsy, or less alert than they are normally. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or are not alert or able to see well.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• Rare
  • Confusion;  hallucinations (seeing, hearing, or feeling things that are not there) 
  
  

• Symptoms of overdose
  • Drowsiness (severe);  shortness of breath or troubled breathing;  unusual tiredness or weakness (severe) 
  
  

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of the following side effects continue or are bothersome:

• More common
  • Drowsiness 
  
  

• Less common or rare
  • Blurred vision;  dizziness;  dryness of mouth;  headache;  heartburn;  nervousness, restlessness, or trouble in sleeping;  skin rash;  stomach upset or pain;  unusual tiredness or weakness  
  
  

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.