Involve large numbers of patients (1000s), usually on a global scale, and are used to compare the efficacy and safety of the new drug with either the standard existing treatment or placebo (dummy treatment). Phase III studies are usually randomised and blinded so that the patients (and the doctor in the case of double-blind clinical trials) do not know which treatment they are receiving to avoid a biased interpretation of the results. Data obtained from phase III clinical trials are used to demonstrate the benefits of the new treatment over existing treatment or placebo.

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