Clinical trials are prospective studies conducted on humans to determine the safety and effectiveness of a newly developed treatment, drug, diet, or medical device. Clinical trials are conducted in different phases. Some early-stage trials may examine the drug's effectiveness and side effects. In later stages, tests are conducted to find out whether the new treatment is better than the existing one. Traditionally, clinical trials are conducted in four phases. Phase I trials involve healthy volunteers to get early data on new treatment methods in human pharmacology and decide the dose or range of doses. Phase II trials involve patients with a disease to explore the safety and efficacy of the new treatment. Phase III trials are therapeutic confirmation studies involving several thousand patients over a short time. Following the completion of phase III trials, the sponsor submits a report to regulatory agencies for marketing approval. Phase IV studies explore therapeutic use after a drug has been approved and marketed to populations with several other conditions, such as patients with compromised liver functions and taking several concomitant medications.