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Phase 4 (post-marketing)

Phase IV is a postmarketing surveillance trial, also known as a drug monitoring trial, which aims to assure the long-term safety and effectiveness of a drug, vaccine, device or diagnostic test[1]. Phase IV trials involve safety surveillance (pharmacovigilance) and ongoing technical support of a drug after it receives regulatory approval to be sold[2].

The drug development process normally proceeds through all four phases of clinical trials over many years[1]. If a drug passes through Phases I, II and III, it will usually be approved by the national regulatory authority for use in the general population[1].

Phase IV studies may be required by regulatory authorities, or the sponsoring company may undertake them for competitive reasons, such as finding a new market for the drug[3]. Other reasons include that the drug may not have been tested for interactions with other drugs, or in certain population groups such as pregnant women, who are unlikely to subject themselves to trials[3].

The safety surveillance is designed to detect rare or long-term adverse effects over a much larger patient population and a longer time period than was possible during the Phase I-III trials[2]. Drugs are approved on the basis of clinical trials involving relatively small numbers of people selected for that purpose, who normally do not have other medical conditions that may exist in the general population[4]. Postmarketing surveillance can therefore refine, confirm or deny the safety of a drug once large numbers of people with a wide variety of medical conditions use it[4].

Why it matters to investors

Harmful effects discovered by Phase IV trials may result in a drug being withdrawn from the market or restricted to certain uses[5]. Following a company's pipeline therefore includes recognising that safety questions can remain open after approval, because surveillance covers a much larger population and a longer period than the earlier trials[2].

On this site

Related: Phase 3 trial, New Drug Application (NDA), Biologics License Application (BLA), EMA marketing authorisation

Sources

  1. "The drug development process" . US Food and Drug Administration. 4 January 2018. Archived from the original on 26 August 2019 . Retrieved 17 August 2020 . web.archive.org (via Wikipedia: Phases of clinical research)
  2. "Types and phases of clinical trials" . American Cancer Society. 18 August 2020 . Retrieved 15 September 2020 . cancer.org (via Wikipedia: Phases of clinical research)
  3. "Step 3. Clinical research" . US Food and Drug Administration. 14 October 2016. Archived from the original on 22 November 2014 . Retrieved 1 February 2017 . web.archive.org; "Types and phases of clinical trials" . American Cancer Society. 18 August 2020 . Retrieved 15 September 2020 . cancer.org (via Wikipedia: Phases of clinical research)
  4. McNeil JJ, Piccenna L, Ronaldson K, et al. (2010). "The Value of Patient-Centred Registries in Phase IV Drug Surveillance" . Pharm Med . 24 (5): 281– 288. doi : 10.1007/bf03256826 . S2CID 19091146 . Retrieved 2011-06-17 . {{ cite journal }} : CS1 maint: deprecated archival service ( link ) adisonline.com (via Wikipedia: Postmarketing surveillance)
  5. Bhattacharya S (25 January 2005). "Up to 140,000 heart attacks linked to Vioxx" . New Scientist . Retrieved 16 February 2026 . newscientist.com (via Wikipedia: Phases of clinical research)

Checked 8 October 2026. How we check sources