Sally Satel says a whole lot of physicians prescribe placebos. Not actual sugar pills or saline, but things like vitamins, Tylenol, or antibiotics that don't actually treat the conditions. In the case of antibiotics, which build up resistance, this strikes me as clearly immoral. But what about the other kinds?
I was actually prescribed a placebo once, after I showed up at the emergency room with a cluster of bizarre symptoms like tingling hands and roaring blood pressure. The ER people clearly thought I was having a panic attack. (I wasn't. Before, after, and during the attack, I was perfectly calm, except for a moment when I realized that my symptoms sounded a lot like those described in the brochure on heart attacks in women that the ER had helpfully provided for me to peruse while waiting.) They told me my potassium was low and gave me some pills.
Unfortunately, I was somewhat familiar with the symptoms of potassium deficiency; mine weren't, mostly, among them. Also, the intern was an incredibly bad liar. I left the ER feeling indignant and not at all improved. Much, much later I found out that tingling hands and high blood pressure are symptoms of thyroid disease, which I do have.
But if I hadn't known, the placebo might have improved me--the mind is a marvelous thing. Here's the thing though: it really wouldn't have been a good idea for me to walk around thinking that an actual medical problem was a potassium deficiency, because then I wouldn't have gone to other doctors to get it treated. Instead, I would have walked around popping potassium pills every time I felt funny.
Doctors give placebos to people they're having a hard time diagnosing. But doctors aren't God. The reason you can't diagnose someone may be that their problem is transient, or imaginary. But it might also be that you've missed something.