The Use of Diphenhydramine (Benadryl) After Surgery

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Diphenhydramine is most commonly known by the brand name Benadryl. This drug is typically used to decrease minor symptoms of allergic reactions, like itching and watery eyes. Diphenhydramine is frequently used after surgery, too, as it can help stop itching caused by various prescription pain medications.

Although most people can take Benadryl safely, this drug is known to cause drowsiness—sometimes to the point of falling asleep. Because of this risk, it's important not to drive or operate heavy machinery while under the influence of diphenhydramine. Diphenhydramine should never be mixed with other sleep aids, alcohol, or certain drugs that could enhance drowsiness, either.

This article discusses the use of Benadryl before and after surgery, including how to take it, its side effects, and potential risks.

A shirtless man holding his stomach in pain
 Stockbyte / Getty Images

Usage Before and After Surgery

It may seem strange to take Benadryl to assist with the surgery recovery process, but this drug can be very useful in the hours and days following surgery. 

Diphenhydramine is frequently given before and after surgery to prevent a very common complication of surgery: nausea and vomiting. Studies have shown that, when used with other medications that prevent this unpleasant side effect, diphenhydramine is very effective for prevention and treatment.

For other individuals, diphenhydramine is given to reduce the itching that people may experience when taking prescription pain medications.

Other Uses

This medication is also used to treat and prevent motion sickness, to reduce the symptoms of Parkinson’s disease, and to reduce cold and flu symptoms.

Many people use diphenhydramine as a sleep aid rather than its intended use, and it is found in some over-the-counter sleep aids.

How Benadryl Works

When you have allergies, your immune system "overreacts" to the presence of a suspected allergen. In an attempt to rid the allergen from your body, the immune system uses the chemical messenger histamine to stimulate allergy symptoms, such as runny nose, itchy throat, and hives.

Benadryl is an H1 receptor antagonist, meaning that it blocks histamine from binding to H1 histamine receptors in the body. In doing so, Benadryl effectively cuts off histamine's ability to trigger allergy symptoms.

How It’s Administered

Benadryl can be taken orally, as a liquid, a pill, or a fast-melting tablet. It can also be given through an IV or as an injection into the muscle. It can also be purchased as a topical spray.

Diphenhydramine can be purchased over the counter to be taken by mouth or to spray on the skin, but injectable forms of the drug require a prescription.

Side Effects

Diphenhydramine has several notable side effects, including:

  • Dizziness
  • Drowsiness and sedation
  • Loss of coordination
  • Dry mouth, nose, and throat
  • Constipation
  • Upset stomach
  • Dry eyes
  • Blurred vision
  • Daytime drowsiness or a "hangover" feeling the day after use

Stop using diphenhydramine and call a healthcare provider right away if you experience:

  • Pounding heartbeat
  • Painful or difficult urination
  • Little or no urinating
  • Confusion
  • Feeling like you might pass out
  • Tightness in your jaw or neck
  • Uncontrollable movements of your tongue

Newer antihistamines are available that decrease these side effects, which is beneficial to those who experience allergy symptoms but want to avoid feeling sleepy.

Risks

Although uncommon, some people may have an allergic reaction to diphenhydramine. Get emergency help right away if you develop signs of an allergic reaction, such as:

  • Hives
  • Difficulty breathing
  • Swelling of your face, lips, tongue, or throat
  • Coughing, wheezing, or shortness or breath

Benadryl is generally considered safe and effective for most people. There are a few exceptions, however. Do not use Benadryl if you:

  • Are breastfeeding: Benadryl is considered safe to use during pregnancy, but there is less information about using it when breastfeeding. If you are breastfeeding, talk to your healthcare provider before taking this medication.
  • Have certain medical conditions: Diphenhydramine should be avoided by those who have glaucoma, prostate problems that make urination difficult, and those with serious breathing issues unless approved by their healthcare provider.
  • Use sedatives: Diphenhydramine should not be combined with other sedatives, including alcohol.
  • Take MAO inhibitors: MAO inhibitors can intensify and prolong the drying effects of diphenhydramine.
  • Drive or operate heavy machinery: Do not operate heavy machinery or drive when taking diphenhydramine due to the risk of drowsiness, lowered alertness, and loss of coordination.

Not everyone experiences drowsiness with this medication, some individuals can have the opposite reaction and may feel jittery or overly excited. This effect is more common in children. Children under the age of 6 should not be given this medication without first discussing it with their healthcare provider.

Misuse of antihistamines increases the risk of severe side effects and overdose. Due to the risk of enhanced drowsiness and/or overdose, Benadryl should never be combined with:

  • Other drugs that contain diphenhydramine
  • Opioids, including Oxycontin and Vicodin
  • Sleep aids, including melatonin and Unisom
  • Benzodiazepenes, including Xanax
  • Alcohol

Summary

Benadryl (diphenhydramine) is a medication primarily used to reduce allergy symptoms. Your healthcare provider may tell you to take Benadryl if you feel nauseous, or if your pain medications make you feel itchy. While Benadryl is effective for reducing these symptoms, it can also make you feel drowsy or sleepy. Therefore, you should never drive or operate heavy machinery while under the influence of diphenhydramine. Take care to only use Benadryl as directed.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Jennifer Whitlock, RN, MSN, FN
Jennifer Whitlock, RN, MSN, FNP-C, is a board-certified family nurse practitioner. She has experience in primary care and hospital medicine.