| Phase | Description |
| I (drug discovery and development) | Studies are conducted to find efficacy, appropriate dosage, methods for administration, side effects, metabolism, excretion and drug interactions |
| II (preclinical studies) | Drug is tested in vivo and/or 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, and about 70% of these drugs move on to the next clinical research phase. |
| Phase 2: Involves up to several hundred people with condition of interest. Lasts few months to two years. Used to monitor the efficacy of the drug, as well as note side effects. Only 30% drugs move to the next phase. | |
| Phase 3: Involves 300-3000 volunteers and can last up to four years. It is used to continue monitoring the efficacy of the drug, as well as exploring any longer-term adverse reactions. About 25% to 30% of drugs move to the next phase. | |
| Phase 4: Involves several thousands of volunteers who have the disease or condition and 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) | Available for sale, safety monitoring continues. |