Glossary of Pharmacology 

Phase III clinical Trial

The Phase III clinical trial is the final pre-approval phase of clinical studies and involves comparing the new drug to either a placebo treatment or to the current standard of care. Phase III trials involve larger groups of patients, which can range from several hundred up to 30,000 people.  The subjects are assigned randomly to the drug or to the control group and are blinded as to whether they receive the new drug or the control treatment.  The aim of this trial is to confirm the effectiveness of the drug/treatment, ideally compared to current “gold standard” treatment, and to continue to monitor its adverse effects.  

Phase III clinical trials are often multi-centre studies (i.e. they are conducted in several locations across a country, or in multiple countries) in a large group of people. 

Phase III clinical trials usually last longer than phase I and II trials. 

Phase III clinical trials are usually the final stage of drug trials before a drug is submitted for approval (i.e. to the U.S. Food and Drug Administration) for subsequent implementation and clinical use. 

While Phase III studies include the evaluation of drug safety, they are often under-powered to detect infrequent serious adverse drug effects.  

Teaching Tips:  

Why do Researchers do Different Kinds of Clinical Studies? https://www.nih.gov/sites/default/files/health-info/clinical-trials/infographic-why-researchers-different-kinds-clinical-studies.pdf  

What is Clinical Research? — YouTube(link is external)  

Types and Phases of Clinical Trials: https://www.cancer.org/cancer/managing-cancer/making-treatment-decisions/clinical-trials/what-you-need-to-know/phases-of-clinical-trials.html  

University of Toronto learning module: https://experientialmodules.utoronto.ca/wp-content/uploads/articulate_uploads/Drug-Development/story.html 

Linked terms:  Generalizability, Sample population, Phase I clinical trial, Phase II clinical trial, Phase IV clinical trial, Clinical trial, Placebo, LOAEL (Lowest Observed Adverse Effect Level), NOAEL (No Observed Adverse Effect Level) 

Resources:  

U.S. Department of Health and Human Services. (2022, October 3). The basics. National Institutes of Health. https://www.nih.gov/health-information/nih-clinical-research-trials-you/basics#:~:text=Phase%20I%20trials%3A%20Researchers%20test,safety%20and%20identify%20side%20effects  

Return to Glossary