What is the deal with fentanyl?

I was broke. Again. During my last year of medical school interest rates were 13%, so yet another loan was out of the question. I took a job at Herfy’s Hamburgers (home of the Hefty Burger) in Seattle. I wore a paper cow on my head.

That wasn’t quite enough, at $2.75 an hour, so I participated in medical experiments, getting paid to have bone marrow biopsies (not worth it), upper endoscopies with no anesthesia (worse), and a weekend taking cold medicine.

One experiment sounded intriguing—all I had to do was wear some monitors and suck on a lollipop. A fentanyl lollipop. The idea was that child...