Phase I is carried out with up to 5 of the original 10,000 substances. It has been shown that over 99% of the original substances are not suitable for further development.
Phase I clinical studies are the first step in testing a new clinical drug in humans. In these studies, researchers evaluate what dose of the drug is safe, how a new drug should be administered (e.g. orally or by injection) and how frequently (e.g. three times a day). The researchers watch very closely for any side-effects that the volunteer may experience.
For some target diseases, it is unethical to conduct Phase I studies in healthy volunteers, due to the toxic side-effects of the Candidate, such as clinical drugs developed to treat HIV and Cancer. Therefore, Phase I studies in these clinical drugs will be carried out in patients who have the target disease.