The preclinical phase of drug development refers to testing of activity and toxicity of a drug candidate in in vitro and in vivo studies before testing in patients can be performed.

The preclinical development stage begins when a viable candidate for formal preclinical development has been chosen. The programme is informed by guidance documents issued by regulatory agencies and includes CMC, animal toxicology, pharmacological data, and clinical protocols and investigator information. The goal of preclinical development is to submit data for review to the regulatory agencies to approve clinical testing of the drug in humans.