During Phase III, the drug or treatment is administered under expanded, controlled and uncontrolled conditions in trials of 1,000-3,000 or more persons. They are conducted only "after preliminary evidence suggesting effectiveness of the drug has been obtained" (Understanding clinical trials, 2006, NIH). These studies conduct cost or risk-benefit analysis of taking the drug and compare the benefits of the drug or treatment to existing options (Understanding clinical trials, 2006, NIH). A drug may be effective, but its side effects may be far more severe than current treatments, and if it provides no additional benefit than existing treatments, the drug may not be approved. Information is also collected to determine when the drug is safe to use, and under what conditions. For example, certain drugs such as MAOIs cannot be taken with other drugs or eaten with certain foods without causing severe health problems; some sedating medications should not be taken when the user will be driving within a few hours.
At the final phase, Phase IV, "studies are done after the drug or treatment has been marketed to gather information...
These trials are conducted after the drug has been released to the public, given that possible side effects and reactions may only be spotted after individuals have been taking the drugs for long periods of time. Additionally, the continued efficacy of the drug should be monitored, as some drugs may produce short-term benefits but sharply decrease in efficacy, with increased user tolerance.
References
What are clinical trial phases? (2006, October 11). FAQ: Clinical Trials. National Institute of Health (NIH). Retrieved November 17, 2001 at http://www.nlm.nih.gov/services/ctphases.html
What is a clinical trial? (2006, October 11). FAQ: Clinical Trials. National Institute of Health
(NIH). Retrieved November 17, 2001 at http://www.nlm.nih.gov/services/ctclintrial.html
Understanding clinical trials. (2006). National Institute of Health (NIH). Retrieved November
17, 2001 at http://clinicaltrials.gov/ct2/info/understand#Q19
