It&#x27;s a problem of testing the efficacy of going through treatment (with any substance, inert or active) vs testing the efficacy of a certain active drug. In double-blind experiments, where placebo effects are attempted to be disentangled from actual drug effects, such a baseline would introduce too many variables to be taken in account. There are psychological factors related to the participants response (&quot;Hey, I joined this clinical trial, but I&#x27;m not being given anything, what&#x27;s up with that?&quot;) that make it difficult to conclude anything from the results. The participant might even be adversely afflicted by this seeming &quot;lack of care&quot; from the experimenters side. Next to that, experiments might experience observer-expectancy effects, where the expectations of experimenters cause the participants to behave in certain ways.<p>Also, if a positive result was found in the &quot;not given any drug&quot; vs &quot;given the active drug&quot; trial, one would still not be sure if this was due to the participant going through the treatment, or due to the treatment + the effects of the drug.