III and IV Phases of clinical trials

III Phase of clinical trials

If the drug is effective and safe in Phase II, it is examined in Phase III. Clinical Phase III trials are carefully controlled studies designed to determine the safety and efficacy of a drug under conditions close to those in which it will be used if it is approved for medical use.


  • determine the short-term and long-term safety / efficacy ratio for dosage forms of the active ingredient
  • determine its general and relative therapeutic value
  • Specific characteristics of the drugs
  • Investigate the profile and varieties of the most common adverse reactions

Usually, the studies have a comparative design in relation to the existing standard therapy (or placebo in the study of a new class of drugs).

Depending on the objectives of the specific study, controlled studies with placebo, reference medication or standard treatment are carried out at this phase. Tests can be either blind or open. Can be carried out in this or that design.

IV Phase of clinical trials

Conducted after the drug was registered for certain indications and becomes available through the retail network. These are the so-called post marketing trials, are conducted on a very large number of participants and are used to determine new modes of drug intake, identify new side effects, etc., provide more detailed information about the safety and efficacy of the drug.


In phase IV clinical trials, the efficacy and safety of registered drugs are studied or clarified within the limits for which medical use is permitted.

If a question arises about a new drug form of the drug, it is decided through Phase III.

Phase IV studies can be used for:

  • Improvements in drug dosage schemes
  • different terms of drug treatment
  • interaction with food or other medicines
  • comparative analysis with other standard courses of treatment
  • use of the drug in other age groups or in patients of other categories
  • effects of long-term effects of the drug on survival (decrease or increase in mortality)
  • long-term results in patients of different groups

IV phase is sometimes confused with postmarketing surveillance — monitoring the safety of registered drugs. Part of the IV phase trials is included in the monitoring process when they are observational in nature and are not experimental. In fact, Phase IV tasks include the study of effectiveness in addition to safety.