If you look at the autopsy data of pilots killed in aviation accidents the No. 1 drug found in their bloodstreams is diphenhydramine.

It is marketed as Benadryl® and a host of other brand names. You would think the most common killer would be something like marijuana, cocaine or other drugs of abuse, not that they didn’t pop up.

But no, it’s common, old, you-can-buy-it-at-any-drugstore Benadryl®. Its generic name is diphenhydramine and it’s been around since 1946. It is one of a number of medications known as antihistamines.

They work, as you’d imagine, by blocking the mediator...