Clinical studies are conducted in order to evaluate the safety and efficacy of a medical treatment (which includes pharmaceuticals, medical devices, and other types of products), procedure, intervention, or policy change. Clinical studies are conducted using human volunteers (often called "participants") and their results are meant to add to medical knowledge.
Clinical studies are grouped into two groups: clinical trials and observational studies.
Participants in a clinical trial receive specific interventions according to the research plan created by the clinical investigators. Interventions include medical products, such as drugs or devices; procedures; or changes to participants' behavior, such as diet. The safety and efficacy of these interventions are typically compared against a standard medical approach (if one exists) or against a placebo.
The status or progress of clinical trials is sometimes referred to as the "Phase" of the trial. In the United States, trial phases are defined by the Food and Drug Administration (FDA):
- Early Phase 1 – Phase of research used to describe exploratory trials conducted before traditional Phase 1 trials to investigate how or whether a drug or device affects the body. These studies typically involve a limited number of human participants and have no therapeutic or diagnostic goals; they're meant to test safety and efficacy. Early Phase 1 trials with human participants typically take place after more rigorous safety and efficacy studies in animal subjects (often called "pre-clinical studies").
- Phase 1 – A research phase to define clinical trials that concentrate on a drug's safety and effective dosage. They are mainly performed with healthy volunteers, and the aim is to evaluate the drug's most common and severe adverse reactions and, sometimes, how the drug is broken down and excreted by the body. A limited number of participants are typically included in these trials. Phase 1 clinical trials typically consist of 20 to 100 healthy volunteers. Approximately 70 percent of drugs move to the next phase.
- Phase 2 – A phase of research to describe clinical trials which gather preliminary data on the therapeutic efficacy of a medical intervention in treating or mitigating the effects of a specified condition or disease. These studies typically compare an intervention (such as a drug) against a different treatment, which is usually an inactive substance (e.g. a placebo). Phase 2 clinical trials may include up to several hundred people with the same disease or condition. Approximately 33 percent of drugs move to the next phase.
- Phase 3 – A phase of the research process wherein more information about a drug's safety and efficacy is collected. The primary purpose of Phase 3 trials is to monitor efficacy and identify side effects and other forms of adverse reactions. Phase 3 studies typically entail giving a drug or other intervention to volunteers from different participant populations (based on factors like age, gender, genetic diversity, pre-existing conditions, and use of other drugs) to further understand efficacy and safety of a drug. Phase 3 trials typically involve between 300 and 3,000 volunteers who have the disease or condition targeted by the intervention being tested. Phase 3 clinical trials can last between 1 and 4 years. Approximately 25-30 percent of drugs move on to the next phase.
- Phase 4 – A phase of research used to describe clinical trials occurring after the FDA has approved a drug for marketing and sale to the public (either over the counter or by prescription). These trials gather additional information about drug safety, efficacy, or optimal use. Phase 4 trials consist of several hundred or several thousand volunteers with the disease or condition targeted by the intervention and may occur at any point in the duration of a drug's time on the market.
In observational studies, investigators evaluate health outcomes in groups of volunteer participants according to a research plan or protocol. Participants receive interventions or procedures as part of their medical care, but participants are not assigned to specific interventions by the investigator (as one would do when conducting a clinical trial). An example of an observational study would be to assess how personal lifestyle choices affect risk for cardiac disease.
There are many types of clinical research and the methods and procedures investigators use can depend on what the researchers are studying. Here are examples of different types of clinical research:
- Treatment Research typically involves an intervention such as a drug, psychotherapy, new medical devices, or new approaches to surgery or radiation therapy.
- Prevention Research aims to find better ways to prevent disease and disorders from developing or coming back. Preventions can include medicines, vitamins, vaccines, minerals, or lifestyle changes.
- Diagnostic Research looks for better ways to identify a particular disorder or condition.
- Screening Research aims to find the best methods to detect certain disorders or health conditions.
- Quality of Life Research finds ways to improve patient comfort and the quality of life for people with a chronic illness.
- Genetic studies try to improve the prediction of disorders by identifying and understanding how genes and illnesses may be related, such as whether a gene, set of genes, or mutation could increase risk for developing a condition.
- Epidemiological studies seek to identify causes, patterns, and control of disorders in groups of people. These studies can investigate non-communicable diseases (like most forms of cancer) as well as infectious diseases (such as a virus or bacterial infection outbreak).
