There are four phases in a clinical trial. The first three phases are the ones most commonly known.

Every time the trial enters a new phase, the knowledge about the medicine and its safety and effectiveness grows.

Phase I

The first phase of a clinical trial is done with a small group of people (about 20-80) for a first evaluation. The researches do a first check of the drug’s safety, determine how much medication should be given, and see if there are any side effects and what they might be.

Phase II

In the second phase, the study drug or treatment is given to a larger group of people (around 100 to 300 people). The purpose is to see how effective it is, and compare how it works for different people. In this phase, researchers also continue to investigate the safety of the medication or treatment.

Phase III

In the third phase of a clinical trial, a large group of people is given the study drug or treatment. Normally, 1.000 to 3.000 people participate in this phase. The large amount of people helps confirm the drug’s  effectiveness, monitor side effects, and compare it to commonly used treatments on a bigger scale. Researches also use this phase to collect and analyse the results to find out how the the medicine or treatment can be used safely.

Phase IV

In the trial’s fourth phase, the drug or treatment is approved for marketing. It’s also made available for an even larger group of people than in Phase III, which means that long-term effects and possible side effects can be analyzed better. The fourth phase has to go on for at least two years, and determines if the medication or treatment is safe and works long-term.

After the trial

As the trial draws to a close, the research done in all the phases is collected and analyzed. The results from a clinical trial help health companies get closer to a possible cure for different conditions. Clinical trials are also helpful for future patients, as they bring new treatments and medication to more people at a faster rate.