Final answer:
The placebo effect occurs when people's expectations or beliefs influence their experience, even if the treatment they receive is inactive. By using a control group that receives a placebo, researchers can control for the placebo effect and distinguish the effects of the drug itself.
Step-by-step explanation:
The phenomenon described in the question is known as the placebo effect. The placebo effect occurs when people's expectations or beliefs influence their experience, even if the treatment they receive is inactive, like a sugar pill or saline solution. In a drug study, both the experimental group receiving the actual drug and the control group receiving the inactive substance can initially show improvement due to the placebo effect.
By using a control group that receives a placebo, researchers can control for the placebo effect and distinguish the effects of the drug itself from the effects of participant expectations. Blinding is often used in drug studies to ensure that both the researchers and the participants do not know who is in which group, further reducing bias and experimenter effects.