That's why it's normal these days, for clinical studies, for the control group to receive current best available treatment, rather than a placebo.
After all, what you're generally trying to find out is whether the new treatment is better than what you already have - just being better than a placebo isn't very informative.
If you're interested in this sort of thing, I strongly recommend reading Ben Goldacre's work[1].
> That's why it's normal these days, for clinical studies, for the control group to receive current best available treatment, rather than a placebo.
That's one of the reasons such studies are so unreliable -- they depend on a comparison of two or more drugs that may operate in different ways, rather than comparing a drug to the absence of a drug.
The result is predictable -- unbiased meta-analyses show that antidepressants don't work:
This is not to say that wouldn't have been the outcome anyway, regardless of the methods used, only that testing two drugs at once introduces confounding factors.
After all, what you're generally trying to find out is whether the new treatment is better than what you already have - just being better than a placebo isn't very informative.
If you're interested in this sort of thing, I strongly recommend reading Ben Goldacre's work[1].
[1] Start at badscience.net.