In an experiment where one participant will be given a treatment medication and another participant will be given a false treatment, the false treatment is called?

A procedure or medicine given to a patient believed by the practitioner to be of no physiological effect is called a placebo.
The benefit comes from the fact that the recipient belives that it will help.
"Mother will kiss it and make it better" is probably the first effective placebo each of us ever received.

...Firstmate