The whole idea of giving a placebo is to trick the patient. If you tell him/her, as lucy points out, it ain't gonna trick anyone.

I suspect the doctors are only going to use a placebo where there's no available (or affordable) medicine that will work and the patient is awkward or insistent, such as Redhead's ex mother-in-law, or just to make the patient think that something is being done, even though it isn't - and maybe can't be (... is that the same thing?).

Anyway, I don't see it as harmful, and it's only deceitful in the same way as saying to a patient suffering from a terminal disease, We're doing everything we can to make you better ...