How do clinical trials progress?

Stages/phases of a clinical trial

Clinical trials go through four phases, each designed to answer a separate research question and improve the prospective treatment.

Phase one

Phase one clinical trials are the first time a new product is tested with humans. The trial happens in a small group of people, normally about 20 to 100, with the goal of determining its safety, and what dosage range will be most effective.

This phase generally takes several months.

Phase two

Phase two progresses to a larger group of people, typically several hundred. This phase is working to determine the benefit of the product, ongoing safety, and how the product is used.

This phase can take from several months up to multiple years.

Phase three

Phase three is the final stage before the product can be used by the public. The study progresses to a larger group, this time several hundred to several thousand people.

Phase three studies confirm efficacy and monitor long-term effects, collecting information that helps the intervention to be used safely.

This phase can run from two years up to a decade.

Phase four

At phase four, the product is approved and being used by the public. Studies continue, with clinical trials monitoring the effectiveness in the general population.

As further information and data are collected, phase four may also investigate potential to use the product in different conditions or in different combinations.