Most drug candidates that reach clinical trials still fail, and one of the biggest reasons is that the models used to test them don't behave enough like human biology. A new generation of tools—patient-derived organoids, spheroids, microphysiological systems (MPS), and organ-on-chip platforms—is closing that gap. But their real power isn't in replacing any single method. It's in knowing which model answers which question, and building a strategy that moves from simple, high-throughput screens to complex, human-relevant systems as the stakes rise.