Tab. II.

Phases of a randomized controlled trial of a drug.

Phases	Aim	Number of participants
Phase 0	To check the capacity of a new drug to modulate its intended target in humans metabolisation of a drug	a few volunteers
Phase I	To check safety and unexpected effects safe dose absorption and elimination by the body	20-80 healthy volunteers or patients in an advanced stage of disease
Phase II	To assess safety and effects in a broader population	Hundreds of volunteers
Phase III	To assess efficacy check for collateral effects compare with pre-existing treatments determine whether approval and commercialization are possible	Hundreds to thousands of volunteers
Phase IV	To collect more information on risk benefits potential uses of an existing drug	Hundreds of thousands of volunteers