Understand clinical trials: from discovery to therapy

The life of a medicine starts many years before it becomes available for general use.

One critical step in this process is a clinical trial. A clinical trial is a type of research study that can help provide that proof. In general, clinical trials are designed to add medical knowledge related to the diagnosis, treatment, and prevention of diseases and medical conditions. Clinical drug trials provide the scientific proof that an investigational drug is both safe and effective for human use.

In some trials, some participants may get a placebo (a pill or liquid that has no active ingredients, like a sugar pill) instead of the drug being studied. Using a placebo gives researchers something to compare with the drug being studied. Usually, participants and researchers will not know which participants are being treated with a placebo or the drug being studied during a clinical trial.

Every clinical trial follows an action plan or protocol.

It describes in detail how the research will be done, including:

  • Who can participate
  • How long the study will run
  • Which tests, procedures, medicines, and doses will be used
  • What information will be collected

Clinical trial protocols must be reviewed and approved by a group of experts called an Institutional Review Board (IRB). The IRB includes doctors, researchers, and members of the community. At the start, and all through the research, the IRB helps ensure that the research is ethical, and that the rights and welfare of the people who are part of the study are protected.

During the clinical trial, the results may be reviewed by an independent team of experts called a Data Safety and Monitoring Board (DSMB). They check for any concerns related to the safety of the drug. The DSMB can recommend to the FDA or the drug company that the study be stopped at any time if it is not effective, is harming participants, or is unlikely to serve its scientific purpose.

Clinical trial phases

Clinical trials typically follow three specific steps, or phases. The phases of clinical trials help researchers collect different types of information. Numbers of participants are frequently smaller in clinical trials for drugs that treat rare diseases.

Testing with a small group 
(generally 20-80 people)


Testing with a larger group 
(generally several hundred people)

  • WHO? Patients who have the disease

Testing with an even larger group 
(generally 300-3,000 people)

  • WHO? Patients who have the disease

The process from clinical trial to drug approval by regulatory authorities can take many years.

Measurement in clinical trials

All clinical trials have "endpoints." Endpoints measure the desired outcomes of the trial. This is often the benefit of a medicine to a patient.

Typically, researchers use either clinical or surrogate endpoints.

Clinical endpoints are generally the most reliable way to measure response in clinical trials. They directly measure the ability to feel better, function better, or live longer.

Surrogate endpoints are often biomarkers that are used instead of clinical endpoints in some clinical trials. A biomarker is a physical, biochemical or genetic characteristic that can be objectively measured.

Learn more about biomarkers used in Duchenne clinical trials, such as dystrophin, from United Parent Projects Muscular Dystrophy.

Common questions about clinical trials