First-in-man study followed by phase II clinical trial
Phase II
Once a dose or range of doses is determined, the next goal is to evaluate whether the drug has any biological activity or effect.  Phase II trials are performed on larger groups (50–300) and are designed to assess how well the drug works, as well as to continue Phase I safety assessments in a larger group of volunteers and patients.  Genetic testing is common, particularly when there is evidence of variation in metabolic rate.  When the development process for a new drug fails, this usually occurs during Phase II trials when the drug is discovered not to work as planned, or to have toxic effects.
Phase II studies are sometimes divided into Phase IIa and Phase IIb. There is no formal definition for these two sub-categories, but generally: