Symptomatic and disease-targeting studies may draw from overlapping early-stage populations, specialist sites, and referral networks. Sponsors that assess this competition before study launch will be better positioned to enroll efficiently and protect data qualit

Consider a person recently diagnosed with Parkinson’s disease. Their symptoms remain relatively mild. They are treatment-naïve or have had only limited exposure to dopaminergic therapy. They receive care from a movement-disorder specialist, are interested in clinical research, and, in consultation with their physician, may be able to take part in a study before their treatment needs change.

To one sponsor, this person may be a candidate for a symptomatic monotherapy study. To another, they may be eligible for a trial of a potential disease-modifying therapy. Depending on their genetics and biomarker status, the same specialist practice may also be identifying people for research that moves earlier still, before a traditional clinical diagnosis.

Eligibility criteria across these studies often overlap, and some seek essentially the same participants. Even where criteria differ, the studies may depend on the same limited research ecosystem: experienced investigators, specialist site capacity, referral networks, and narrow eligibility windows. That shared dependence creates a risk of recruitment collision that traditional feasibility may not capture.

Two Pipelines, One Early Population

The September 2026 FDA approval of JUVMO™ (tavapadon) is a timely reminder that early-stage populations remain central to symptomatic drug development. According to the prescribing information, JUVMO is a once-daily, oral, non-ergot dopamine agonist indicated for the treatment of Parkinson’s disease in adults. The prescribing information describes tavapadon as a selective partial agonist at the dopamine D1 and D5 receptor subtypes.

Its two Phase III monotherapy trials, TEMPO-1 and TEMPO-2, enrolled adults with less than three years of diagnosed Parkinson’s disease who were treatment-naïve or had received less than three months of prior dopaminergic therapy. TEMPO-2 randomized 304 participants across 75 sites in 13 countries, about four per site. TEMPO-1 randomized 529 across 102 sites in 12 countries, about five per site. These averages are not a direct measure of competition, since per-site yield also depends on factors such as country mix, study duration, and when each site was activated. They do show the reach a narrowly defined early-stage population may demand.

Meanwhile, disease-modifying and prevention research is moving earlier. A 2025 review, Preparing for Parkinson’s Disease Prevention Trials: Current Progress and Future Directions, identifies participant selection, intervention timing, and biomarker strategy among the central challenges of trials conducted before a conventional diagnosis.

We see the operational implications of this shift firsthand as clinical operations partner for The Michael J. Fox Foundation for Parkinson’s Research’s Path to Prevention platform trial, which recently reached its first FDA protocol milestone. The central lesson extends beyond any single study: moving earlier requires an ecosystem capable of finding potential participants, confirming biological eligibility, communicating uncertainty responsibly, and sustaining engagement over time.

Three Clocks, One Narrow Window

A prevalence estimate is not an enrollment forecast. Each requirement, from time since diagnosis and prior treatment to biomarker status and site access, narrows the population. As explored in our article, Parkinson’s Is Not One Disease. Why Are We Still Designing Trials as If It Is?, a broad diagnostic label can conceal the characteristics that determine whether someone fits a specific protocol.

Eligibility is also temporary, because three clocks run at once in an early-stage Parkinson’s trial.

The disease clock tracks change in symptoms, function, and underlying biology.

The treatment clock marks when the participant and physician decide symptomatic therapy should begin or change.

The trial clock runs through screening, randomization, follow-up, and endpoint collection.

These clocks do not stay aligned on their own. A participant can become ineligible by starting a prohibited therapy, exceeding a disease-duration limit, progressing beyond the permitted range, or enrolling in another trial. A long screening pathway can let the window close, and a late endpoint may be affected by treatment changes that were foreseeable when the protocol was written.

Sponsors cannot stop the disease or treatment clocks to protect the trial clock. They can design studies that anticipate how all three will move.

Five Ways to Plan for Recruitment Collision

1. Conduct competitive feasibility

Experienced movement-disorder centers attract many sponsors at once, and a site may reasonably report the same potential population to each of them. Sites also have good reason to present that population favorably: they are asked about many studies, and cannot be sure they will be selected or that every study will start. When feasibility starts from diagnosed patients rather than those who meet the combined criteria, several programs can end up forecasting on the same people.

Participants, meanwhile, choose freely and voluntarily which study to join, if any. A site with several open trials can offer patients more options, but no single protocol can count on that site’s whole pool. A competitive assessment should cover:

  • Eligibility and treatment-window overlap with other active or planned studies, including those testing different mechanisms
  • Investigator and coordinator capacity, and how each site prioritizes across its trials
  • Access to imaging, laboratory, and biomarker services
  • Competition at country and regional level, to identify regions with suitable populations and fewer competing studies

Refresh the assessment before activation and again during enrollment. The picture used for site selection may have changed by the time a site is ready to recruit.

2. Stress-test eligibility criteria

Evaluate each criterion individually and in combination, separating requirements essential to safety and interpretability from those carried over from earlier protocols. The Clinical Trials Transformation Initiative’s 2025 recommendations on using real-world data to plan eligibility criteria and enhance recruitment offer a useful framework: confirm data are fit for purpose, model how criteria shape the eligible population, and involve patients and sites early. Site input is especially valuable on whether a criterion can be applied consistently without unnecessary screening burden.

3. Build referral pathways before sites fall behind

Many potential participants first see community neurologists, primary care clinicians, or sleep specialists, and reaching them earlier can identify candidates before the eligibility window closes. Define responsibilities early: sponsors and CROs map referral opportunities, prepare materials, and remove administrative barriers, while sites build trusted relationships and keep referring physicians informed.

A good pathway lets a community clinician refer without feeling they are surrendering the clinical relationship. Relationships built only after enrollment falls behind rarely develop that trust.

4. Reduce burden that does not strengthen the evidence

Procedures that are safe and scientifically justified can still deter enrollment or erode participation. A 2025 community-based study of people from groups historically underrepresented in Parkinson’s research found respondents less willing to join studies requiring intravenous infusions or lumbar punctures, and identified transportation and financial support as facilitators.

Sponsors can ask whether screening can be sequenced more efficiently, whether routine follow-up can move to remote or local settings, and whether digital measures replace clinic assessments or merely add to them. The guiding question is whether each demand materially strengthens safety, interpretability, or the scientific objective.

Where a demanding procedure is essential, how it is delivered matters too. A 2025 Parkinson’s Progression Markers Initiative analysis in Clinical Parkinsonism & Related Disorders, following participants for up to 13 years, found serial lumbar punctures to be safe, but compliance fell from 90% at baseline to 56.2% at year five and 35.7% at year nine. A successful first procedure was the strongest predictor of long-term compliance, while a procedure-related adverse event within seven days of the baseline lumbar puncture was associated with lower long-term compliance. That makes the first procedure, including site training and participant preparation, part of retention planning.

5. Plan for changing treatment needs

Some participants will need to start or adjust symptomatic therapy during the study. That is a predictable part of an early-stage Parkinson’s trial, not protocol noise. The protocol and statistical analysis plan should define in advance:

  • When additional treatment is permitted
  • Whether participants remain in follow-up, and which assessments continue
  • How post-treatment data contribute to the analysis
  • How many participants are needed to maintain statistical power, given the decisions on symptomatic treatment
  • How these expectations are explained during informed consent

The ICH E9(R1) training materials on estimands and sensitivity analysis explain how treatment initiation and other intercurrent events can be addressed by aligning the clinical question with trial design, data collection, analysis, and interpretation.

Recruitment Strategy Is Competitive Strategy

The approval of JUVMO is a reminder that early-stage populations remain essential to symptomatic development. The growing focus on disease modification and prevention means more programs may depend on the same early identification, specialized infrastructure, and precisely defined participants.

Not every study competes for the same individual, but many draw on partly overlapping pools. Sponsors can no longer assess feasibility as though each program enters an isolated research landscape.

That also means seeing the choice from the patient’s side. People weigh what a trial asks of them against what it may offer, including the potential benefit of the investigational treatment and continued access afterward. An open-label extension, for example, can make a study more attractive. Patient-centered design is therefore not only good practice but a recruitment advantage.

Everyone may want the same patient. The programs best positioned to reach that patient will be those designed around what the patient needs next.