Male scientist in lab

Clinical trial phases

Clinical trials are governed by strict regulation. Throughout each trial, the proceedings are monitored by government authorities as well as GSK’s own Global Safety Board (GSB).

There are always at least three phases to clinical trials. Occasionally a fourth phase might be necessary if:

  • we think the medicine can be improved
  • we need to provide answers to questions from the regulatory authorities

Phase I

The first time a new treatment or vaccine is tested in humans, it will usually be given to a small group of healthy volunteers. However in some cases—such as when a new medicine is being tested as a treatment for a terminal illness like cancer—it may be tested on volunteers who have the condition.

The principle objectives in Phase I are to:

  • make sure that the new medicine presents no major safety issues
  • clarify that it can reach the targeted body area, and remain there long enough to deliver its benefits
  • gain preliminary evidence that it could offer therapeutic value, or prevent the disease or condition

Phase II

If Phase I is successful, approval will be sought for a trial involving a larger group of people. Phase II trials will usually (but not always) include patients who have the condition the potential medicine is targeting, and aim to establish:

  • effectiveness in treating the condition
  • effectiveness in preventing the condition (if the volunteer does not already have it)
  • appropriate dosing levels

At this stage, the performance of the medicine may be compared against a group of patients receiving a placebo. A placebo is a treatment that looks the same as the potential new medicine, but has no active ingredients.

In this way a reference group is established against which the performance of the new medicine can be judged. It is important that neither the patients nor the researchers have any idea which volunteers receive which treatment. This is known as double blind placebo control, and ensures there can be no bias in the reporting of the results.

Phase III

If the results from Phase II are encouraging, we will seek to start a Phase III trial. This will be a much larger trial, often involving hundreds, possibly thousands of participants coming from a range of different countries.  

The principle objectives in Phase III are to:

  • demonstrate the safety and effectiveness of the new medicine or vaccine in the typical patient likely to use it
  • confirm effective dosing levels
  • identify side effects or reasons why the treatment should not be given to people with the condition in question (known as ‘contraindications’)
  • build knowledge of the benefits of the medicine or vaccine and compare them with any risks
  • compare results against any currently achieved by existing treatments

To be a success today, a new medicine usually needs to offer the prospect of better treatment for patients than any treatments that are already available.

Phase III trials may last several years. If a new medicine or vaccine completes Phase III with positive results, we may seek regulatory approval to make it available in a range of countries or regions.

In the case of a new medicine, regulators will determine how it should be used, and which patients should qualify for it, based on all the evidence from clinical and pre-clinical studies. This is known as a medicine’s indication.

Monitoring medicines after launch

Monitoring is overseen by our Global Safety Board (GSB), which is chaired by our Chief Medical Officer and made up of senior physicians and scientists.

Part of the GCB’s responsibility is to review the information on the safety of our products as reports come in from patients and prescribers on the use of the medicines.

All the Board's decisions are guided by the need to ensure that the benefits of our medicines and vaccines always outweigh any risks. We continue to monitor patients' responses to our medicines through reports and regulator reporting systems. We follow this information to understand fully a new medicine's safety and effectiveness. We also look for any adverse effects that may only become apparent as more patients use a treatment.