The various phases of clinical trials

A clinical trial is conducted according to a study protocol set in advance. A trial may last from a couple of weeks up to a year or more, depending on the question, the disease, the nature of the therapy and how easy or difficult it is to recruit study participants.

The results from clinical trials constitute an important part of the documentation required to get a medicine approved for sale. Often, it is also a requirement that companies or researchers carry out trials of the safety of a medicine even following an approval.

Phase 1

Phase 1 often uses healthy study participants, around 20–80 individuals who are usually men, to study the safety of the product. A substance is investigated for any side effects, how the body breaks it down and disposes of it, and what the pharmacological characteristics are. Phase 1 starts by testing a very low dose of a substance, and the dose is then gradually increased. Between each increase, a comprehensive safety evaluation is made. For phase 1, or first-in-human as these studies are also called, there are special EU-common guidelinesexternal link, opens in new window.

Phase 2

For Phase 2, study participants are recruited who have the disease or condition that is to be treated with the therapy in question. The number of study participants is still limited, and the patient group should be as homogenous as possible. During Phase 2, a first idea is obtained of the effect of the therapy on a certain disease, and the optimal dose. The new therapy is compared with existing therapies or placebo, and further information about the safety of a substance and any side effects is also obtained.

Phase 3

During Phase 3, large patient groups of between 200 and 3 000 individuals or more are studied, to confirm the effect and pattern of side effects of a therapy compared to standard therapy or placebo over a longer period. The dose used is the one found most suitable during an earlier phase. The patient groups shall resemble as far as possible the group on which the finished therapy will be used (for example gender, weight and age). So-called “interaction studies” are also carried out, where the reactions to the substance in question of patients who are simultaneously receiving other therapy are looked at.

If the Phase 3 studies are successful, an application can be made to have the therapy approved.

Phase 4

Once the product has begun being marketed, major studies are carried out to map unusual side effects and to monitor the safety, effectiveness and optimal area of use of the therapy.