Most common clinical trial therapy areas

As of May 2025, there are 22,985 clinical trials recruiting patients in the U.S., according to the National Library of Medicine (NLM). Another 10,296 are active and longer recruiting.

While clinical trials are FDA-mandated for all new treatments-including drugs, medical devices, vaccines, and gene therapies-these studies also produce crucial data used in making other care decisions. In addition to evaluating the safety and efficacy of new treatment options, clinical trials can help both providers and manufacturers determine which medical approaches work best for certain illnesses or patient populations.

What are the different types of clinical trials?

Clinical studies are classified into two main groups based on the research protocol and whether or not participants receive medical interventions as part of their testing. These categories are defined as:

• Interventional studies (more commonly referred to as clinical trials)
  Investigators assess participant health outcomes based on specific interventions administered as part of the research protocol in order to test the safety and effectiveness of a candidate drug, therapy, or experimental treatment.
• Observational studies
  Investigators assess participant health outcomes as established in the research protocol without administering interventions or procedures.

Within this framework, clinical studies can be further segmented by subtype-including prevention, treatment, diagnostic, screening, genetic, epidemiological, or quality-of-life trials.

Definitive Healthcare tracks both interventional and observational trials across 14 different therapy areas. Data is compiled from The Clinical Trials Transformation Initiative (CTTI) and can be viewed in our HospitalView, PhysicianView, and PhysicianGroupView products. In this blog, we've compiled a list of the top 10 most common clinical trials by therapeutic area.

Top 10 clinical trial therapeutic areas

Fig. 1 Data from the Definitive Healthcare Atlas Dataset and sourced from The Clinical Trials Transformation Initiative (CTTI). The total number of clinical trials includes all historically reported. Accessed May 2025.

Cancer treatments have the highest clinical trial volume

Treatments for cancer have the highest number of clinical trials by therapeutic area - 25% of all trials analyzed. With an increasing number of new cancer drugs being developed each year, this clinical trial volume can be expected to grow.

Clinical trials for mental health and behavioral disorders represent 15.1% of the trials analyzed. From antidepressants and anti-anxiety medications to emerging psychedelic options, our mental health treatment choices continue to expand.

Next, trials for nervous system diseases, endocrinology and metabolic disease, including diabetes, and cardiovascular and circulatory diseases each represent more than 10% of the clinical trials on the list. Other top therapeutic areas by clinical trial volume include:

• Infectious diseases
• Respiratory diseases
• Digestive diseases

Where do clinical trials take place?

Below, we mapped the number of clinical trials by each state. The analysis includes 36,576 active clinical trials listed on ClinicalTrials.gov, which are those identified as "recruiting," "not yet recruiting," "active," and "not recruiting."

Clinical trial volume by state