In clinical trials, what is the function of a placebo?

• A. Provide active therapy
• B. Act as a non-active comparator
• C. Test for side effects only
• D. Replace treatment during later phases

Answer: (B)

The key idea is that a placebo serves as a non-active comparator to isolate the true effect of the experimental treatment. By giving an inert substance that looks and feels the same as the active therapy, researchers can blind participants and sometimes investigators, reducing bias from expectations. This setup lets them compare outcomes between the active treatment and the placebo group to see what portion of any improvement is due to the treatment itself rather than placebo effects or natural disease changes. The other options miss the main purpose: a placebo does not provide active therapy, its role isn’t to test side effects alone (even though side effects can be observed in both groups), and it isn’t used to replace treatment in later phases.