Which phase involves the introduction of a drug for the first time in human subjects?

Phase 1 trials are specifically designed to assess the safety, tolerability, pharmacokinetics, and pharmacodynamics of a drug when introduced to human subjects for the first time. During this phase, a small group of healthy volunteers or patients is involved, which allows researchers to gather critical data on how the drug interacts with the human body without the confounding factors of prior exposure or long-term use.

The primary goal is to determine the highest safe dose and to identify potential side effects. This early stage is crucial because it lays the groundwork for further testing in subsequent phases, where the drug’s effectiveness is evaluated against different conditions and larger populations. In contrast, the subsequent phases (2 and 3) focus more on efficacy and side effects that may arise in a more diverse cohort, while phase 4 involves post-marketing surveillance to understand long-term effects after a drug is on the market. Thus, Phase 1 is distinct due to its pioneering nature in human trials.