Costs of Clinical Trials, page-5

Sort of disagree, I think only phase 2 will hints us whether the drug has any efficacy. Phase 1 is just "safe to use", works or not dunno.

PhasePrimary goalDosePatient monitorTypical number of participantsSuccess rate^[2]Notes

Phase ITesting of drug on healthy volunteers for safety; involves testing multiple doses (dose-ranging)often subtherapeutic, but with ascending dosesclinical researcher20–100 normal healthy volunteers (or for cancer drugs, cancer patients)approximately 70%determines whether drug is safe to check for efficacy