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Clinical Trials

Clinical trials are an essential step in the medicine development process.

Clinical Trial Data and Results

At Pfizer we believe researchers, trial participants, regulators, and others acting in the best interest of patients should have access to clinical trial data to advance medical understanding and promote data transparency.

That’s why we publicly share results from our clinical trials, whether the results are neutral, negative or positive. In line with regulatory requirements, we are committed to transparency, and publish information about the purpose of each trial, the eligibility of patients to join the trial and the location of the study.

There are several ways in which we share trial results and data in the UK:

What is a Clinical Trial?

A clinical trial is a research study that explores whether a medical treatment or device is safe and effective for humans. It plays a critical role in the process of bringing new therapies to patients.

On average it takes over 10 years for a potential new therapy to be developed and approved for use with patients,although the time varies greatly depending on the complexity and success of the new therapy. Whilst the development of a vaccine to combat COVID-19 was achieved in an unprecedented timeframe of under a year, it relied on two decades of earlier research and development.Similarly, the first gene therapy took more than 20 years before being approved by the European Union.3

Trials conducted during clinical development generate thousands of pieces of data that are generally used by regulatory agencies, to determine approval for use of the therapy and in which medical indications.

Patient Volunteers

Clinical trials rely on hundreds to many thousands of volunteer trial participants. For patients suffering from a condition that is currently untreatable, enrolment in a clinical trial may provide access to potential new therapies. While participating, volunteers are closely monitored by trial researchers, and their involvement in such trials will help others by contributing to medical research. Every trial is governed using well-defined ethical rules and standards to protect participant safety.

Clinical Trial Process

Pre-clinical studies
Before testing on humans, early trials are carried out on the most promising molecules, using computer simulations (in silico studies), cell-based tests (in vitro studies) and animal tests (in vivo studies). Only if the molecule meets specific safety standards and demonstrates value as a potential new therapy, does it progress to clinical testing in humans known as 'Phases'.

Phase 1: Small number of healthy volunteers4
Phase 1 trials usually focus on ensuring the therapy is safe to use in people, rather than how effective it may be as a treatment for a given disease. During this phase, escalating doses of the experimental therapy are given to a small number of study participants so that researchers can measure the body’s response, including how it is absorbed, its duration in the bloodstream, and which dosage levels are safe and well tolerated.5

Phase 2: Larger group of people with the disease4
Phase 2 trials generally assess the effectiveness of an experimental therapy at treating a specific illness or medical condition.

Information about the experimental therapy's safety, side effects, and potential risks are also collected. In this phase, researchers work to determine the most effective dosages for the experimental therapy and the most appropriate method of delivery, such as tablets, extended-release capsules, infusions, or injections. Phase 2 clinical trials involve a larger number of trial participants, typically up to several hundred, who usually have the medical condition that the experimental therapy is intended to treat.

Phase 3: Typically thousands of patients4
Phase 3 trials test the results of earlier trials in much larger groups of people and gather additional information on the effectiveness and safety of the experimental therapy.

This phase will usually involve several hundred to several thousand participants across multiple study locations. These trials are often randomized, where participants are randomly allocated to receive the experimental therapy, placebo, or an existing treatment. Trials are often "double-blinded" in which neither the investigator nor the participant are aware if the therapy given is the true experimental therapy, placebo, or an existing therapy. Phase 3 trials generally provide the primary basis for the benefit–risk assessment for the new therapy and much of the core information about the therapy that is analysed for inclusion in final labelling if approved by the regulatory authority.

Licensing approval
Results from clinical trials are submitted to regulatory agencies to obtain a licence prior to it being made available to patients. The European Medical Agency (EMA) is responsible for regulatory approval of new drugs within the European union (EU), whilst the Medicines and Healthcare products Regulatory Agency (MHRA) is responsible within Great Britain. After a drug has been approved by the EMA or MHRA, health assessment bodies like the National Institute for Health and Care Excellence (NICE) and the Scottish Medicines Consortium (SMC) assess whether the treatment can be made available for routine use on the NHS.

Phase 44
Also known as "post marketing studies", ongoing monitoring is required after regulatory approval and is critical to informing the ongoing use of the therapy. Through such trials, researchers collect additional information about longer-term risks, benefits, and optimal use. These trials often involve thousands of participants and may continue for the lifetime of the drug.

Pfizer Clinical Trials in the UK

During 2021 within the UK, 27 Pfizer clinical trial protocols were in place, across 71 clinical trial sites with 234 enrolled patients.5

As part of our INSPIRE programme (Investigator Networks, Site Partnerships and Infrastructure for Research Excellence), we have built a trusted network of preferred locations for clinical trial research, which now spans over 90 sites around the globe, with 6 located in the UK.

Find a UK Trial

The National Institute for Health Research (NIHR) provides a comprehensive list of clinical research studies running in the UK.


Global Regulatory Affairs

After successful clinical trials, new medicines or treatments need to be licensed and approved before they can be made available to patients.


Pfizer Pipeline

Globally, our scientists are committed to transforming molecules to medicines in order to improve the lives of millions of people around the world.


  1. PhARMA. Research & Development Policy Framework. Sept 2021.
  2. Nature, December 2020. The lightning-fast quest for COVID vaccines — and what it means for other diseases
  3. NCBI, January 201. Gene therapies development: slow progress and promising prospect
  4. NHS UK May 2019, 'Clinical Trials'
  5. Pfizer data on file. December 2021
    PP-UNP-GBR-2837 / December 2022
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