Pharmaceutical researchers use two groups of subjects to prove if a specific drug is effective.
In clinical trials, one group is given the actual drug. This group is called the "experiment group". The other group, called the "control group" is given a sugar pill.
Both groups are told they are given a drug and that they should start feeling the effects of it.
They are then monitored at intervals to document the effects of the drug.
When participants in the control group react as if the drug is real, this is called the "placebo effect".
The mere fact that they been given a suggestion they believe in, gives their subconscious permission to allow for the effects of the drug.
This is a pretty strong statement in regards to how powerful suggestion are.
Most studies done have indicated that the belief in treatment combined with the expectation of the outcome strongly effects the results.