The stages a candidate must pass | Visual AI Learning Guide

Think of this as a one-way street. At the top, discovery and design produce a candidate molecule aimed at a chosen target. Then preclinical testing checks it in cells and animals. Only if it survives that does it reach people, and even then it moves through three separate phases: first a small safety check, then a first look at whether it helps patients, then a large confirmation. After that comes regulatory review, and finally monitoring that continues once the drug is actually being prescribed. The important thing to notice is the direction of the arrows. Nothing skips a stage, and nothing moves backward.

0:00 / 0:00

Auto-play

A drug candidate does not move from idea to prescription in one step. It passes through a fixed sequence of stages, and each stage has a different job.

Discovery and design produce a candidate molecule aimed at a chosen biological target. Preclinical testing checks that candidate in cells and animals for safety and basic behavior. If it survives, it enters clinical trials in humans, which run in three phases: Phase I for safety in a small group, Phase II for a first signal of benefit in patients, and Phase III for confirmation of benefit in a large group. A successful drug then goes through regulatory approval, where authorities review the evidence and decide whether it may be sold. After approval, post-approval monitoring continues to watch the drug in ordinary use.

The order matters because each stage is a gate. A candidate that fails at any gate does not continue, and the later the gate, the more time and money have already been spent.