In which phase of the drug approval process is the new drug compared to an existing drug or placebo?

The phase of the drug approval process where the new drug is compared to an existing drug or placebo is Phase II. This stage primarily focuses on evaluating the drug's effectiveness while continuing to assess its safety. In Phase II trials, participants are usually patients who have the condition that the drug is intended to treat, allowing researchers to gather data on how well the drug performs compared to existing treatments or placebo.

Phase I is designed primarily to assess safety and dosage in a small group of healthy volunteers without a focus on comparing the drug's effectiveness against other treatments. Phase III typically involves larger populations and is often the final stage before seeking regulatory approval, focusing more on confirming effectiveness and monitoring side effects in more diverse groups. Phase IV, or post-marketing surveillance, occurs after a drug is approved and is used to monitor long-term effects and safety, rather than comparing the drug directly against other therapies or placebos in the manner described.