This common over-the-counter drug was the precursor to Prozac. It can make you drowsy, scramble your brain, and impair your driving more than alcohol.

Thanks to an abundant crop of grapes last summer I had hundreds of yellow jackets swarming around my patio and was stung twice. The first time I ignored the sting on my thigh and woke up the next morning with a large (ham-size), painful and blistered swelling which severely limited my movement for two days. After the second sting, which was on my neck (dangerous!), I immediately took some Benadryl in both pill and cream form, and had almost no reaction. While I was delighted with the lack of reaction to the sting, I was dismayed by the way the Benadryl made me sleepy and disoriented, and scrambled my brain for a couple of days.

Benadryl was the First Popular Antihistamine
Benadryl, or diphenhydramine, has been around since 1943 when it was created by a chemical engineer at the University of Cincinnati, who took it to the drug company Parke-Davis for development. This was the first effective antihistamine developed that didn’t cause extreme drowsiness, and it proved to be a blockbuster drug. In the ensuing decades it was commonly prescribed for sniffling sneezing-type allergies, hives, insect stings, sleep, sedation, anxiety, cough and cold symptoms, motion sickness and nausea. Meanwhile, scientists noticed that the antihistamines often elevated mood, and created the first generations of antidepressants. In the mid-1970s, the diphenhydramine molecule was tweaked to create Prozac, the first selective serotonin reuptake inhibitor (SSRI) antidepressant.

In the 1980s the FDA made diphenhydramine an over-the-counter drug and topical cream, and it enjoyed new status as an allergy drug. Since then other allergy drugs that don’t cause sleepiness have become more popular, but Benadryl is still widely advertised as a seasonal allergy medicine, and diphenhydramine is the most common ingredient found in dozens of over-the-counter sleep medicines. For example, it is the active ingredient in Compoz, Nytol, Sominex and Unisom Sleep Gels. Tylenol PM is a combination of acetaminophen and diphenhydramine, and Excedrin PM is a combination of aspirin and diphenhydramine. It is also a popular ingredient in cough and cold medicines such as Tylenol Flu NightTime, Hydramine Cough Syrup, and Sine-Off.

Although diphenhydramine is undoubtedly still the home medicine cabinet first-drug-of-choice for wasp and bee stings and other severe allergic reactions, it’s a mystery why it is so easily available and recommended for regular use. This is a serious drug that interacts dangerously with many other common medications and causes enough drowsiness in most people to make driving risky. In addition to the above uses, it’s prescribed to control involuntary movements caused by other medications and by early Parkinson’s.

Common Side Effects of Diphenhydramine
Common side effects of diphenhydramine include dry mouth, nose, and throat, drowsiness, dizziness, nausea, vomiting, loss of appetite, constipation, increased chest congestion, headache, muscle weakness, excitement (especially in children), nervousness, dizziness, vision problems (especially blurred vision) difficulty urinating and painful urination, and erectile dysfunction.

It can cause a variety of rapid and irregular heartbeats, short-term memory loss, hallucinations, irritability, confusion and delirium, twitching and muscle spasm.

If you mix this drug with alcohol or with virtually any other drug that is sedating or causes sleepiness, the effects will be exaggerated and could be dangerous.

Diphenhydramine and Driving
According to the National Highway Traffic Highway Association (NHTHA), “Diphenhydramine has repeatedly been shown to severely impair tracking and reaction time performance in actual on-the-road driving tests. … The authors concluded that diphenhydramine clearly impairs driving performance, and may have an even greater impact than does alcohol on the complex task of operating a motor vehicle.”

The NHTHA performance evaluation states that, “Laboratory studies have shown diphenhydramine to decrease alertness, decrease reaction time, induce somnolence [sleepiness], impair concentration, impair time estimation, impair tracking, decrease learning ability, and impair attention and memory within the first 2-3 hours post dose. Significant adverse effects on vigilance, divided attention, working memory, and psychomotor performance have been demonstrated. It is important to note that impairment has been shown to occur even in the absence of self-reported sleepiness or sedation. Concurrent use of diazepam [e.g. Valium] and diphenhydramine caused significant performance decrements at 2 hours, and to some degree up to 4 hours.”

Keep on Hand for Emergencies and Use with Caution
Diphenhydramine is an important drug to keep in the home medicine cabinet in case of a bad reaction to a bee or wasp sting, or other allergic reactions. However, considering its profound effects on the brain, which can linger for days, it is difficult to understand how this drug could be recommended by any thoughtful health professional for such complaints as seasonal allergies and insomnia, when there are so many better and safer alternatives.

Related Article: Natural Alternatives to Drugstore Medicines for Allergies