Phase 0 clinical trials are human studies and are intended to speed up the development of promising drugs or imaging agents by verifying (early in the phase trials) whether the drug or agent behaves in human subjects as was expected from preclinical studies. Distinctive features of Phase 0 trials include the administration of single doses of the study drug to a small number of subjects (10 to 15) to gather preliminary data on how the body processes the drug (pharmacokinetics) and how the drug works in the body .
   
A Phase 0 study does not supply data on safety or efficacy, because by definition, these studies use doses that are too low to cause any effect.
 

Phase I trials are the first stage of testing in human subjects. Normally, a small (20-80) group of healthy volunteers will be selected. This phase includes trials designed to assess the safety , , , and of a drug. These trials are often conducted in an in-patient clinic, where the subject can be observed by full-time staff. The subject who receives the drug is usually observed until several of the drug have passed. Phase I trials also normally include dose-ranging, also called , studies so that the appropriate dose for therapeutic use can be found. The tested range of doses will usually be a fraction of the dose that causes harm in animal testing.
 

Once the initial safety of the study drug has been confirmed in Phase I trials, Phase II trials are performed on larger groups (20-300) and are intended to assess how well the drug works, in addition to the continuation of Phase I safety assessments in a larger group of volunteers and patients. 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.

 On-going CMCH trials