But the placebo affect has nothing to do with the actual effectiveness of the 'drug'. In general the people who get better while using a placebo would have gotten better had they done nothing.
I cannot imagine a doctor would ever ACTUALLY prescribe a placebo for a patient who was genuinely sick, because the only benefit a placebo may have is causing the patient to THINK they will get better. However, they can still get this benefit by receiving ACTUAL medication, as well as the benefits of the medication itself.
It is also not irrational that placebos do have a percentage of effectiveness, simply because some people do get better, and it is known that a persons state of mind can have an effect on their health.