Merck Manual

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From Laboratory to Medicine Cabinet

From Laboratory to Medicine Cabinet


Test Group



Early development

Laboratory settings (such as cell cultures and animals)

To determine the chemical and physical characteristics of the drug and to assess the safety and effects of the drug in living organisms

2–6.5 years

Clinical studies

Phase 1

20–80 healthy volunteers

To establish basic safety and blood levels achieved with different doses of the drug

1.5 years

Phase 2

Up to 100 people who have or who might develop the disorder being studied

To establish the drug's effectiveness and dosage range and to identify side effects

2 years

Phase 3

300–30,000 people who have the disorder being studied

To confirm the most effective dosage regimen, to obtain more information about the drug's effectiveness and side effects not seen during phases 1 and 2, and to compare the drug with existing drugs, a placebo, or both

3.5 years

FDA review

Government review of all information from early development and clinical studies

To determine whether the drug has been proved to be sufficiently effective and safe

0.5–1 year

Phase 4 (postmarketing surveillance)

All people taking the drug, particularly subgroups such as pregnant women, children, and older people

To identify any problems that did not occur in phases 1, 2, or 3, such as those that take a long time to appear and those that occur rarely