I have seen MDs use the placebo effect ( my family doctor with my son) and discussed it with my MD brother.
He points out the challenges to useing it:
1) You must not lie.
You may say that some people believe this can be helpful but you must not say that it is a wiz bang wonder medicine that cures what ails you.
2) You must be sure that there are no treatable causes of the symptoms.
A thorough work up is required to be sure you know what you are dealing with to the degree possible.
3) You must not make any money from selling it.
This isn't a problem (at least here) since a physician is not allowed to sell what s/he prescribes.
These conditions can make it difficult for an ethical physician to use placebos because:
They work best if they are hyped as being powerful (including discussion non existent side effects (which may then be experienced -- but only if discussed). So lying maybe estential.
The suppliers of these things often aren't able to do a proper diagnosis.
The placebo is likely to be more effective if it is expensive (must be good if it costs a lot) and an ethical pharmacy isn't going to charge $5 per sugar pill.