There are complete five phases of clinical trials but the most important are Phase 1, 2, 3 and these are described as below:
This is the first phase before starting the phase one trials and its main goals is to test the initial idea and to determine the fact if there are any effects. For that purpose they take some initial test of the compound under study to find out if it has any side-effects. These tests are made on animals.
The goal of the phase one is to find a safest treatment, most effective ways to deliver the drugs and evaluating its side effects. These tests are made on healthy patients to find side-effects. The smallest dose that they find with side effects will be the maximum dose used in the remainder of the trial.
This phase of clinical trial is built on the results of phase one. In this phase they introduce the patients with actual disease to the drugs and find out how well the treatment works. Numbers of patients participating in phase two are more than phase one. They move on to phase three depending upon the effectiveness and results of the phase two.
This phase includes thousands of patients where a huge amount of money is spent. They perform randomization and their goal is to see if the new treatment is better than the recent standard of care. This phase can take years because it takes a lot of time to recruit patients.
Drugs are submitted to FDA for further approval when it succeed from phase three and then the phase four starts.
Main goal of phase four is to analyze the consumption of drug on daily basis by the patients and within the market. They find out if it is better or equal to the current standard of care and its impact on the lives of the people.