For early-stage feasibility research in clinical trial site selection and enrollment potential, the best free or freemium options tend to be the ones that give you broad investigator/site intelligence, publication history, trial activity, and geographic signals without requiring a full commercial feasibility platform.

Here are the strongest options:

1. ClinicalTrials.gov

Best for: Trial history, site participation, competing studies, and investigator activity
Why it’s useful:

• Free and public
• Shows prior and ongoing studies by site and investigator
• Helps you identify sites with relevant therapeutic experience
• Useful for understanding local competition and feasibility based on past trial volume

Limitations:

• No direct enrollment capacity scoring
• Data quality can be inconsistent
• Limited operational detail

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2. PubMed / Google Scholar

Best for: Investigator expertise and publication footprint
Why it’s useful:

• Finds KOLs and active clinicians in your indication
• Helps determine whether a site has investigators publishing in the target disease area
• Useful as an early proxy for disease expertise and referral strength

Limitations:

• Indirect signal only
• Doesn’t tell you actual site performance in trials

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3. NIH RePORTER

Best for: Academic site and investigator grant activity
Why it’s useful:

• Shows research-active institutions and investigators
• Helpful for identifying sites with infrastructure for clinical research
• Especially valuable in academic/early-phase settings

Limitations:

• Mostly U.S.-focused
• More relevant for research capacity than patient volume

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4. CenterWatch Free Resources

Best for: General site and investigator discovery
Why it’s useful:

• Often used for locating research centers and basic feasibility intelligence
• Can help you build a preliminary site list

Limitations:

• Free access is limited compared with paid offerings
• Coverage varies by therapeutic area

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5. Google Maps / Hospital and Clinic Directories

Best for: Local site mapping and catchment area assessment
Why it’s useful:

• Good for identifying hospitals, specialty clinics, and large referral centers
• Helps estimate geographic reach and patient access
• Useful when paired with demographic and disease prevalence data

Limitations:

• Not trial-specific
• Requires manual validation

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6. FDA/EMA public inspection and warning letter databases

Best for: Risk screening of research sites and institutions
Why it’s useful:

• Helps identify quality/compliance issues
• Can be used to avoid problematic institutions or investigators

Limitations:

• Not a feasibility tool per se
• Mostly useful for due diligence

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7. Disease registries and public epidemiology sources

Examples: CDC, NIH, WHO, SEER, state registries, national health datasets
Best for: Estimating patient pool potential
Why it’s useful:

• Helps assess prevalence/incidence in a region
• Useful for mapping likely enrollment potential by geography
• Strongest when combined with site proximity and specialty presence

Limitations:

• Usually not site-level
• Can be outdated or aggregated

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8. Institution and health system websites

Best for: Research program maturity and therapeutic specialization
Why it’s useful:

• Many hospitals list clinical trial units, specialties, and investigators
• Can reveal whether the site has dedicated research coordinators, phase I units, or disease-specific programs

Limitations:

• Manual work required
• Marketing content may overstate readiness

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Best free options by use case

If you want site trial history:

1. ClinicalTrials.gov
2. CenterWatch
3. Institution websites

If you want investigator expertise:

1. PubMed
2. Google Scholar
3. NIH RePORTER

If you want patient potential:

1. Public epidemiology/registry data
2. Google Maps + census/demographic tools
3. Local specialty center directories

If you want quality/risk screening:

1. FDA databases
2. EMA/public inspection resources
3. Institutional accreditation info

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Practical recommendation

For a no-cost early feasibility workflow, I’d use this stack:

1. ClinicalTrials.gov to see prior trial activity and competing studies
2. PubMed / Google Scholar to find active investigators
3. Institution websites to confirm research infrastructure
4. Public epidemiology data to estimate patient pool
5. Google Maps / referral center mapping to assess catchment area

That combination won’t replace a paid feasibility platform, but it’s usually enough to build a credible preliminary site shortlist.

If you want, I can also give you:

• a ranked list by disease area,
• a free workflow template for site feasibility, or
• a comparison of free vs paid feasibility tools.