Early clinical development starts when a sufficient amount of nonclinical/preclinical knowledge from experimental studies has accumulated. Especially, the safety and tolerability issues of the candidate drugs are carefully evaluated, and it is essential that these non-clinical laboratory- and animal investigations are continued throughout the clinical development when more information accumulates.

The fate of a drug in the human body (pharmacokinetics) is described and predicted by pharmacokinetic modeling and simulation. The human pharmacokinetics of drugs in early development phases can be studied safely after microdosing. In microdosing studies very low drug doses, much below the pharmacologically effective level, are administered to healthy volunteers.

The brain penetration of drugs targeting the central nervous system is studied using brain imaging (positron emission tomography, PET).

The genetic background of an individual may have significant effect on the drug response in the body. In the early phase, the individual genetic variance of metabolizing enzymes and transporters (polymorphism) is evaluated to clarify the effects on drug metabolism and distribution.