At what phase of clinical trials are healthy volunteers tested for drug safety?

In clinical trials, the process of testing drug safety begins in Phase I, where healthy volunteers are involved in the study. This phase primarily focuses on assessing the drug's safety profile, determining the appropriate dosage, and observing how the drug is metabolized and excreted by the body. The goal is to identify any potential side effects and establish a safety range for the drug before it is tested on individuals who may have the condition the drug is intended to treat.

Phase II, on the other hand, typically involves participants who have the disease or condition and is aimed at evaluating the drug's efficacy and further assessing its safety in a larger group. Phase III expands this evaluation and includes a much larger population to confirm effectiveness and monitor adverse reactions in diverse groups before approval for public use. Pre-clinical studies occur before clinical trials and usually involve laboratory and animal testing, focusing on initial safety and efficacy data before healthy humans participate.

Thus, the correct answer highlights that Phase I is the critical initial phase for safety testing in healthy volunteers.