What occurs during Phase 4 clinical trials?

During Phase 4 clinical trials, the primary focus shifts to the long-term monitoring of a drug after it has been approved for general use. This phase is often referred to as post-marketing surveillance, where researchers and regulatory agencies observe the drug's performance in the broader population.

This phase is crucial because it helps identify any rare or unusual side effects that may not have been evident in earlier phases of clinical testing, where participant numbers are usually fewer and conditions are more controlled. The collection of data during Phase 4 can lead to additional insights into the drug's long-term health risks and benefits, ensuring that ongoing safety precautions are in place and the medication remains effective for the public over time.

The other options pertain to earlier stages of drug development and testing. Initial testing on humans occurs in critical early phases prior to Phase 4, and animal testing is even further back in the research timeline, while confirming the drug's formulation happens before mass distribution, typically in the preclinical and Phase 1 trials.