Other side effects include motor impairment (ataxia), flushed skin, blurred vision at nearpoint owing to lack of accommodation (cycloplegia), abnormal sensitivity to bright light (photophobia), sedation, difficulty concentrating, short-term memory loss, visual disturbances, irregular breathing, dizziness, irritability, itchy skin, confusion, increased body temperature (in general, in the hands and/or feet), temporary erectile dysfunction, and excitability, and although it can be used to treat nausea, higher doses may cause vomiting. Diphenhydramine in overdose may occasionally result in QT prolongation.Some individuals experience an allergic reaction to diphenhydramine in the form of hives.Conditions such as restlessness or akathisia can worsen from increased levels of diphenhydramine, especially with recreational dosages. Normal doses of diphenhydramine, like other first generation antihistamines, can also make symptoms of restless legs syndrome worse. As diphenhydramine is extensively metabolized by the liver, caution should be exercised when giving the drug to individuals with hepatic impairment. Anticholinergic use later in life is associated with an increased risk for cognitive decline and dementia among older people. Contraindications
Diphenhydramine is contraindicated in premature infants and neonates as well as people who are breastfeeding. It is a pregnancy Category B drug. Diphenhydramine has additive effects with alcohol and other CNS depressants. Monoamine Oxidase inhibitors prolong and intensify the anticholinergic effect of antihistamines. Overdose
Diphenhydramine is one of the most commonly misused over-the-counter drugs in the United States. In cases of extreme overdose, if not treated in time, acute diphenhydramine poisoning may have serious and potentially fatal consequences.
This has been met with criticism, both by doctors and members of the airline industry, as sedating young passengers may put them at risk if the flight encounters an emergency and they are unable to react to the situation efficiently, and the drugs side effects, especially the chance of a paradoxical reaction, may result in some individuals becoming hyperactive rather than sedated. The ethics of this use have also been challenged, with the Seattle Childrens hospital arguing in a 2009 article that "Using a medication for your convenience is never an indication for medication in a child. "The American Academy of Sleep Medicines 2017 clinical practice guidelines recommended against the use of diphenhydramine in the treatment of insomnia due to poor effectiveness and low quality of evidence. A major systematic review and network meta-analysis of medications for the treatment of insomnia published in 2022 found little evidence to inform the use of diphenhydramine for insomnia. Nausea
Diphenhydramine also has antiemetic properties, which make it useful in treating the nausea that occurs in vertigo and motion sickness. Special populations
Diphenhydramine is not recommended for people older than 60 or children under the age of six, unless a physician is consulted. These populations should be treated with second-generation antihistamines such as loratadine, desloratadine, fexofenadine, cetirizine, levocetirizine, and azelastine. Due to its strong anticholinergic effects, diphenhydramine is on the Beers list of drugs to avoid in the elderly.Diphenhydramine is category B in the FDA Classification of Drug Safety During Pregnancy. It is also excreted in breast milk.