Clinical trials

A clinical trial is an interventional study: researchers assign participants to receive one or more interventions and examine what happens. Interventions can include medicines, medical devices or behavioral approaches. In an observational study, by contrast, researchers collect information about care or behavior without assigning an intervention. Randomization—assignment by chance—is used in some trials, not all; a trial may have comparison groups, or all participants may receive the intervention under study.

A trial is built around a research question and a written protocol. The protocol specifies who may take part, how many participants are sought, what intervention is given and at what dose, how long the study lasts, which outcomes are measured, and how results will be analysed. When a comparison is needed, a control group may receive standard care, a placebo, or no intervention, depending on the question and what is ethically acceptable. Random assignment and masking can reduce some forms of bias, but the design must fit the intervention, participants and purpose; there is no single template for every clinical trial.

For many medicines and biological products, phases organize successive questions, although some trials combine phases and not every kind of clinical trial has an FDA-defined phase. Early drug studies typically examine how the product behaves in the body and what doses can be tolerated. Phase 2 studies investigate it in people with the relevant condition and gather further safety and early benefit data. Larger Phase 3 studies assess whether a product benefits a defined population while collecting additional safety information. In the United States, Phase 4 studies take place after approval and can add information during broader use. These are broad aims, not guarantees that a product will be effective or safe for every person.

Clinical research involving people requires safeguards as well as scientific design. The World Medical Association's Declaration of Helsinki calls for research protocols to undergo independent ethics-committee review before research begins, and says participation by people able to consent must be voluntary and based on adequate information about aims, risks and burdens. It also calls for human-participant research to be registered in a publicly accessible database before recruitment begins and for results—including negative and inconclusive findings—to be made public. Trial participation may or may not benefit an individual participant; the purpose is to produce evidence while risks are assessed and monitored. Findings should be interpreted in light of the particular participants, intervention and conditions studied.