Diphenhydramine Side Effects, How it Works, Upsides & Downsides

Diphenhydramine is an antihistamine and is used for relieving the symptoms of various diseases like the common cold, hay fever, and allergies such as sneezing, itchy nose or eyes, cough, and runny nose. Other uses also include treating dizziness, vomiting, and nausea due to motion sickness and helping you to fall asleep.


Diphenhydramine blocks histamine, a chemical substance that body produces during allergic reactions. Meanwhile, it is effective for drying symptoms like a runny nose and watery nose as it also blocks acetylcholine produced by the body.

Side effects

In case of an allergy to diphenhydramine, you’ll experience:

  • Difficulty in breathing
  • Hives
  • Swelling of the lips, throat, tongue, and fact
  • Other side effects that diphenhydramine can cause include:
  • Uncontrollable movement of the tongue
  • Tightness in the jaw or neck
  • Confusion
  • Painful urination
  • Difficulty or fluctuation in urination
  • Pounding heartbeat


If such side effects are experienced, stop taking diphenhydramine and contact your doctor. Other common side effects include:

  • Day-time drowsiness
  • Constipation
  • Dry eyes
  • Loss of coordination
  • Blurred vision
  • Upset stomach
  • Dry mouth, throat, or nose


How to take diphenhydramine

As with all medicines, diphenhydramine must be used according to your doctor’s prescription or as instructed on the medicine’s label. Don’t adjust the dosage or the recommended time for the medicine. Medicines for cold and allergy are only taken for a short period until the symptoms clear up.

Diphenhydramine must not be given to kids younger than two. Make sure to consult a doctor before you give a cold or cough medicine to your child as misuse of such medicines in infants and young children can lead to death.


Use a special dose-measuring medicine cup or spoon to measure the liquid.

If you are taking diphenhydramine for motion sickness, then take it half an hour before you’ll be in a situation that causes motion sickness. Continue taking it with meals as well as at bedtime for the remaining part of your motion sickness situation.

If you are taking diphenhydramine to help you sleep, then take it half an hour before your bedtime.



You must avoid diphenhydramine if you are allergic to it, dimenhydrinate, and the other active ingredients of the medicine. Also, make sure that your doctor is familiar with your medical history. Inform him of:

  • Difficulty urinating
  • Glaucoma
  • Heart problems
  • Breathing problems
  • Liver disease
  • Hyperthyroidism
  • Seizures
  • Intestine problems

Diphenhydramine can blur your vision and make you drowsy and dizzy. Thus, avoid taking part in activities that require a clear vision and alertness. Avoid alcohol and marijuana while taking diphenhydramine as they can make you more dizzy or drowsy.


Diphenhydramine in the form of dissolving tablets, chewable tablets, and liquids may contain sugar while the liquid form might also contain alcohol. Therefore, take care if you have a liver disease, diabetes, or phenylketonuria.

Both children and adults might be increasingly sensitive to the side effects. In young children, the medicine might cause excitement instead of drowsiness. On the other hand, older adults might be more sensitive to constipation, confusion, dizziness, and trouble urinating.

During pregnancy, use diphenhydramine if needed. But first, discuss the benefits and risks with your doctor. It is also known to pass into breast milk and cause undesirable effects in a nursing infant. Therefore, caution is advised.