How Do Medical Studies Work?

Medically Reviewed by Carol DerSarkissian, MD on May 29, 2023
4 min read

Medical studies test out new medicines, types of surgery, or medical devices in groups of people. These studies help researchers learn whether new treatments are safe and if they work. If you've ever taken medicine or had surgery, you can be sure that your treatment was tested in a medical study before it reached you.

Medical studies come in two main types:

Clinical trialscompare a medicine, device, or other new treatment against something else, such as:

  • The current medicine used to treat the same disease
  • A "fake" treatment that doesn't contain any active ingredients, called a placebo
  • No treatment

Researchers divide study participants into two groups. One group gets the new treatment and the other one gets the standard treatment for their condition or no treatment. Then researchers compare the results.

Some medical studies look at new methods to prevent or diagnose diseases. Others explore ways to improve quality of life in people with certain conditions.

Observational studies look at what happens when people follow a certain treatment. For example, researchers might compare the health of people who exercise every day with the health of those who don't exercise as often.

A researcher at a hospital, university medical center, or drug company comes up with the idea for a medical study. The researcher then designs the trial to answer certain questions about the treatment. For example, they may want to know whether it works better than current treatments or if it causes side effects.

Studying a new treatment in a clinical trial can cost millions of dollars. That money comes from:

  • Drug or medical device companies
  • University medical centers
  • Nonprofit organizations, such as the Alzheimer's Association or American Cancer Society
  • Government agencies, such as the National Institutes of Health or the U.S. Department of Veterans Affairs

A principal investigator leads every study. That person is often a doctor.

Supporting the principal investigator is a research team made up of:

  • Doctors
  • Nurses
  • Social workers
  • Dietitians
  • Medical students
  • Other health care professionals

Clinical trials take place in:

  • Hospitals
  • University research centers
  • Community clinics
  • Doctors' offices

Some studies will pay for people who live far away from the research site to travel there. The study may cover the cost of airfare, other transportation, and hotels.

People like you. Studies include people of all ages, races, and genders. Some people join a medical study because other treatments they tried didn't work for them. Others join because there is no treatment for their disease.

Before a new treatment is tested on humans, researchers first study it in lab animals to look for any possible safety issues. Only treatments that have a good safety profile move forward into clinical trials.

Medical studies have four phases. Each phase includes larger groups of people.

  • A phase I study includes 20 to 80 people. Its purpose is to find out whether the treatment is safe and to get the dose right.
  • A phase II study includes 100 to 300 people. It looks at how well the treatment works for a certain medical condition.
  • A phase III study includes a few hundred to a few thousand people. It looks at how the treatment works in different groups of people and at various doses. If the results of a phase III study are positive, the FDA may approve the treatment.
  • A phase IV study is done after the FDA approves the treatment, to monitor its long-term safety.


Many steps are involved in getting a new treatment into a clinical trial. It can take 3 to 6 years for researchers just to decide whether the drug is worth studying.

Then a new treatment may spend 6 to 7 years getting through phases I to III of clinical trials. And researchers will continue to monitor the treatment's safety for many months or years after the FDA approves it.

Medical journals publish studies. First, researchers have to find a journal that matches their study. For example, studies published in the Journal of the National Cancer Institute must relate to cancer.

Researchers also need to meet the journal's publishing requirements, which can be strict. Respected journals like TheNew England Journal of Medicine and JAMA receive thousands of research submissions each year and publish only about 5% of them.

Many journals are peer-reviewed to make sure the studies they publish are high-quality. They have doctors and scientists read the studies for quality and accuracy before the journal decides to publish them.

Doctors read medical studies to learn whether a treatment works and if it is safe before they prescribe it to their patients. Studies also show what side effects a treatment might cause, which helps doctors watch for symptoms or avoid the treatment in certain patients.

All of these are signs of a high-quality medical study:

  • It's approved by the FDA, the agency that regulates new drugs, vaccines, and medical devices. The FDA has rules in place to protect people who are in clinical trials.
  • It's reviewed by a group of doctors or researchers who are not part of the trial. These experts monitor the study during the whole process to make sure that it is safe for the people involved.
  • The researchers got informed consent from every person in the study. This means each person received enough information to make an informed decision about whether to participate before they signed on to join.