Scientists have created double-blind studies so that neither the subjects of the experiment nor scientists know whether the subject is receiving an actual drug or a placebo, which is nothing more than a sugar pill  Essentially, if one knows whether one is receiving actual medicine or a placebo, such knowledge can affect the outcome of a study  A recent double-blind study on the effectiveness of the Selective Serotonin Reuptake Inhibitor (SSRI) Freloxamine on depression found that those subjects administered the drug were 15% more likely to have a decrease in symptoms than the control group, which was comprised of those who received a placebo
Since neither group knew which they were receiving, the placebo or the SSRI, the observed drop in depression can only be attributed to Freloxamine
At dosages two-fold of those employed in the trial, Freloxamine has been shown to cause brief episodes of psychosis.