Sure it does. If the scan dye is causing the treatment effect it will show equally in the treatment group and the control group thereby preventing a type 1 error. That is, the drug appearing to be a successful drug when it in fact is not what was causing the treatment success.
The same is true for the other factors I mentioned.
I think you are saying that a control group would not identify the factors causing the apparent treatment effect instead of the drug and that is true.
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