| Phase | Description |
| I (drug discovery and development) | Studies are conducted to determine the drug’s efficacy, appropriate dosage, methods of administration, side effects, metabolism, excretion, and potential drug interactions. |
| II (preclinical studies) | The drug is tested in vivo and/or in vitro to determine its potential for harm (toxicity). |
| III (clinical research) | Phase 1: Involves 20-100 study participants and lasts several months. Used to determine the safety and dosage of the drug. About 70% of these drugs move on to the next clinical research phase. |
| Phase 2: Involves up to several hundred people with the condition of interest. Lasts from a few months to two years. Used to monitor the drug’s efficacy and to identify side effects. Only 30% of drugs move to the next phase. | |
| Phase 3: Involves 300-3000 volunteers and can last up to four years. Used to continue monitoring the drug’s efficacy and to evaluate longer-term adverse reactions. About 25%-30% of drugs move to the next phase. | |
| Phase 4: Involves several thousand volunteers who have the disease or condition. Continues to monitor safety and efficacy. If a drug passes this phase, it goes on to FDA review. | |
| IV (FDA review) | Takes 6-10 months. |
| V (post-market monitoring) | The drug is available for sale, and safety monitoring continues. |