What's Benadryl Doing to Baby Brains?

A new study on nonprescription sleep aids may be a wake-up call .

Posted Jan 30, 2015

You’re pregnant and can’t sleep. Miserable, you ask your doctor what to take. “Diphenhydramine,” you’re told. It’s the active ingredient in over-the-counter sleep aids such as Benadryl, Unisom, Sominex, Exedrin PM, and Tylenol PM. An antihistamine, it’s also commonly taken for colds and allergies.

The FDA classifies diphenhydramine (perhaps best known as "Benadryl") as a “Category “B” drug in pregnancy, meaning that there’s no evidence of risk to fetuses. Why not take it?

Here’s why not. A new study published in JAMA Internal Medicine found that the cumulative use of Benadryl and other similar nonprescription medications is linked with dementia and cognitive impairment in older people. This study is not the first to find a connection, but it’s the largest one to date. The researchers tracked nearly 3,500 people for seven years. Around 800 of them developed dementia by the end of the study, and those who used Benadryl were likelier to have cognitive impairment than those who did not.

In particular, the study estimated that people taking at least 4 mg/day of diphenhydramine for more than three years are at a greater risk of developing dementia. (The average dose of Benadryl for use as a sleep aid is 50 mg.) The drug is an anticholinergic, which works by blocking the action of the neurotransmitter acetylcholine. In the brain, acetylcholine is necessary for learning and memory.

"Wait," you might think. The study participants were seniors. Causality isn’t proven. And the risk, if real, appears to be accumulative.

On the other hand, this study reminds us that science has not really explored the effects of Benadryl and the like on the brains of fetuses, infants, or children. Might the same anticholinergic properties have an effect on a baby’s developing nervous system? If the drug contributes to dementia and loss of cognitive function late in life, what might it be doing to the brain early in life when forming its neural infrastructure? Might prenatal exposure only show up later in life? Even a minor decrease in cognitive function would be alarming.

This study warrants a good, hard look at the effects of over-the-counter anticholinergic drugs on the developing brains of fetuses, babies, and children. If I were a doctor, I’d urge my pregnant and pediatric patients to consider alternatives.

The fact that we now know that this drug may impair the elder brain but haven’t yet explored its effect on the young brain ... if I were pregnant again and took it, I don’t think I’d be able to sleep.

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