This is usually done in three phases. A phase one study takes several months and focuses on the drug's safety. The drug is tested on a small number of people, usually 20 to 100 healthy individuals.
Doctors study how the drug is absorbed, metabolized, and excreted.
This phase often also includes studies of side effects that occur as dosage levels are increased. About seventy percent of experimental drugs pass this phase of testing. A phase two study lasts from several months to two years, may involve up to several hundred patients, and is usually conducted as a randomized, blinded trial . During this phase, the pharmaceutical manufacturer is carefully examining the safety and effectiveness of the drug. About one third of candidate drugs successfully complete both phase one and phase two studies.