Diphenhydramine Side Effects: Does Benadryl Cause Dementia?

Last Updated: July 17, 2020

Authored by Sharon Levy, MD, MPH

Diphenhydramine is an antihistamine which is prescribed for conditions such as watery eyes, sneezing, runny nose, fever, and other common symptoms of allergies and flu. Diphenhydramine HCl side effects may result in different health conditions. Read further to find out about various diphenhydramine side effects, how can they be managed and minimized, and what can be done to use diphenhydramine safely.

Diphenhydramine Common Side Effects

Active ingredients in Benadryl are responsible for the various side effects of diphenhydramine, which range from mild to severe. Most common and less serious side effects of Benadryl are listed below:

  • Drowsiness
  • Dizziness
  • Headache
  • Confusion
  • Dry mouth
  • Nasal congestion
  • Fatigue
  • Nausea

Can Benadryl Cause Diarrhea?

Diarrhea is one of the common side effects experienced by patients taking this drug. However, this adverse reaction mostly resolves after taking this medicine for a few days.

Does Benadryl Cause Constipation?

Some patients experience constipation when they start taking Benadryl doses. This is not a severe side effect and can be managed by increasing the amount of fiber intake and taking oral laxatives.

Can Benadryl Cause Anxiety?

Although diphenhydramine is used for the short-term treatment of anxiety, if used for extended periods, it can even cause increased anxiety and other mental changes.
Man sitting in dark room experiencing anxiety disorder

Benadryl Severe Side Effects

There are some severe adverse reactions associated with the use of Benadryl, which should immediately be checked by a doctor. These include:

  • Tachycardia
  • Blurred vision
  • Difficulty urinating
  • Restlessness and lack of concentration
  • Severe dizziness
  • Rash and difficulty in breathing
  • Symptoms associated with a severe allergic reaction

If any of the above rare but severe adverse reactions are experienced, patients should immediately seek medical help.

Long-Term Side Effects of Diphenhydramine

Long term use of Benadryl has been associated with issues of memory loss. Some patients may require it to be used for long periods since their doctors might believe that their benefits outnumber the possible adverse reactions. Long term effects of Benadryl include:

  • Short-term memory losses
  • Dependence
  • Liver Damage
  • Problems in mental cognition
  • Lower blood pressure
  • Vision impairment
  • Dizziness

Does Benadryl Cause Dementia?

Yes. According to this study about the long-term effects of diphenhydramine, patients are at an increased risk of developing dementia when they use diphenhydramine for the long-term. It poses various mental challenges, including dementia, cognitive problems, and concentration issues.
Aged couple holding hands and looking at each other

Benadryl and Alzheimer’s

Benadryl side effects also include Alzheimer’s, primarily when used for longer durations in elderly patients.

Allergic Reaction to Benadryl

Some individuals may be allergic to Benadryl, which might result in some severe side effects.

Does Benadryl Lower Blood Pressure?

One of the side effects of long term use of Benadryl is that it results in an increased heart rate and lower blood pressure in some patients.

Does Diphenhydramine Cause Weight Gain?

Benadryl weight gain has also been reported as it results in an increased appetite in patients when used for long-term. This, in turn, results in weight gain in some patients.

Side Effects of Diphenhydramine in Kids and Adolescents

In kids and adolescents who use Benadryl, allergy plus congestion can be effectively treated. However, it can cause specific adverse reactions for them, which are similar to those experienced by adults.
Little baby boy has allergies and itchy skin
Additionally, children’s Benadryl side effects also include:

  • Increased irritability,
  • Excitement,
  • Insomnia

Benadryl long term use in children can lead to seizures and heart problems. In the case of Benadryl OD, death can also be caused, especially in children due to seizures. Diphenhydramine should only be used in children under the prescription of a qualified doctor.

Minimizing Side Effects of Diphenhydramine

Certain side effects of Benadryl may affect the normal routines of patients. The undesirable effects of Benadryl can be minimized and managed so that patients can continue with their day-to-day activities in an efficient manner. The following tips can be followed to manage these side effects:

  • Diphenhydramine and alcohol should never be taken together, as it will increase the adverse reactions of the drug.
  • Similarly, the use of different pills, like Zyrtec and Benadryl together will result in an overdose which can be dangerous. When taken for short-term in low doses, diphenhydramine can prove to be quite useful to treat various symptoms of allergies.
  • Can one take Benadryl while pregnant? Yes, antihistamines, including diphenhydramine, are deemed safe to be used during pregnancy. Diphenhydramine is also prescribed during pregnancy for morning sickness and nausea. A study on Antihistamine Use in Early Pregnancy was carried out to identify any possible associations of diphenhydramine with congenital disabilities when taken early in the pregnancy. According to its findings, no such association could be identified. No congenital abnormalities or anomalies were detected in women who used diphenhydramine during their pregnancy.
  • However, diphenhydramine is excreted in breast milk, which can result in dangerous adverse reactions in the infant, including seizures. So it should be avoided during breastfeeding.
  • Diphenhydramine sometimes causes drowsiness because it has a sedative effect. The time for which drowsiness lasts depends on the half-life period. Diphenhydramine half-life ranges from 3.4 to 9.3 hours, with an average elimination half-life of 4.3 hours. It is recommended to stay at a low dosage to avoid drowsiness.

Page Sources

  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4592307/
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4140658/

Published on: June 5th, 2019

Updated on: July 17th, 2020

About Author

Sharon Levy, MD, MPH

After successful graduation from Boston University, MA, Sharon gained a Master’s degree in Public Health. Since then, Sharon devoted herself entirely to the medical niche. Sharon Levy is also a certified addiction recovery coach.


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