A clinical trial is any research study that prospectively assigns human participants or groups of humans to one or more health-related interventions to evaluate the effects on health outcomes.
As defined by MedicineNet: Trials to evaluate the effectiveness and safety of medications or medical devices by monitoring their effects on large groups of people. Clinical research trials may be conducted by government health agencies such as NIH, researchers affiliated with a hospital or university medical program, independent researchers, or private industry.
Usually volunteers are recruited, or in another cases research subjects may be paid. Subjects are generally divided into two or more groups, including a control group that does not receive the experimental treatment, receives a placebo (inactive substance) instead, or receives a tried-and-true therapy for comparison purposes.
Typically, government agencies approve or disapprove new treatments based on clinical trial results. While important and highly effective in preventing obviously harmful treatments from coming to market, clinical research trials are not always perfect in discovering all side effects, particularly effects associated with long-term use and interactions between experimental drugs and other medications.
Clinical trials are conducted in a series of steps, called phases - each phase is designed to answer a separate research question.
Phase I: Researchers test a new drug or treatment in a small group of people for the first time to evaluate its safety, determine a safe dosage range, and identify side effects.
Phase II: The drug or treatment is given to a larger group of people to see if it is effective and to further evaluate its safety.
Phase III: The drug or treatment is given to large groups of people to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the drug or treatment to be used safely.
Phase IV: Studies are done after the drug or treatment has been marketed to gather information on the drug's effect in various populations and any side effects associated with long-term use.
There are four possible outcomes from a clinical trial:
Positive trial -- The clinical trial shows that the new treatment has a large beneficial effect and is superior to standard treatment.
Non-inferior trial -- The clinical trial shows that that the new treatment is equivalent to standard treatment. Also called a non-inferiority trial.
Inconclusive trial -- The clinical trial shows that the new treatment is neither clearly superior nor clearly inferior to standard treatment.
Negative trial -- The clinical trial shows that a new treatment is inferior to standard treatment.