Recruiting patients for Alzheimer’s trials is already a challenge. Some 99% of eligible patients are either never referred to a trial or never consider joining one, according to the World Alzheimer Report 2026 from Alzheimer’s Disease International.
But many who are willing to volunteer are then excluded because of common health conditions.
“Trial protocols can exclude people because of cardiovascular disease, diabetes, a history of stroke, psychiatric conditions or the use of particular medicines,” Paul Gallagher, the report’s lead writer, said in an email, noting that these conditions are common in the older adults who make up much of the Alzheimer’s population.
Patients can also be disqualified if they fall outside the required disease stage or cognitive test score range, or lack qualifying results based on diagnostic tests such as PET scans.
“For some newer treatments, brain scans may identify abnormalities that make participation unsafe. These exclusions can be medically justified, but they also narrow the pool of eligible participants considerably,” he said.
Screening, therefore, eliminates a high percentage of applicants. On average, 44% of patients screened for mild Alzheimer’s trials and 88% of those screened for trials in preclinical Alzheimer’s disease, which enroll asymptomatic patients, don’t qualify, according to the report. This trend could slow research into Alzheimer’s disease as drug development ramps up after decades of setbacks.
At the start of 2026, nearly 160 potential therapies were being tested in 192 active Alzheimer’s trials, creating demand for about 55,000 participants, according to the report. But given the rejection rates, filling those slots would require at least 350,000 people to come forward for screening.
The problem isn’t unique to Alzheimer’s: Older adults have long been underrepresented in other fields, such as cancer trials.
“The concern is that we end up studying a relatively select group of people, rather than the diversity of patients seen in everyday clinical practice,” Gallagher said. “If we want treatments that work for the wider population, we need to ensure that clinical trials are as representative as possible of the people who may eventually benefit from them.”
Here, Gallagher expands on the challenges facing these complex trials and potential solutions to increase enrollment.
Responses have been edited for style and brevity.
PHARMAVOICE: How can sponsors and investigators determine whether inclusion and exclusion criteria are necessary for participant safety and scientific validity, or whether they could be made more flexible?
PAUL GALLAGHER: The starting point should be to ask a simple question when it comes to eligibility criteria: What is the evidence that this restriction is necessary, and what would be the consequence of relaxing it?
There are legitimate reasons to exclude people from a study, particularly where there are safety concerns. With anti-amyloid treatments, for example, the risk of amyloid-related imaging abnormalities, including brain swelling and bleeding, means that medical history, MRI findings and certain medications require careful consideration. We should not dilute safeguards simply to recruit participants more quickly.
But there is a difference between a restriction that is essential for safety and one that has become embedded in a protocol because it has always been there. Sponsors and investigators should review criteria systematically, drawing on clinical evidence, previous trial data and the experience of people who have been screened but excluded.
Could a wider range of common medical conditions be accommodated with appropriate monitoring? Could age limits be reconsidered? Could cognitive assessments be adapted to account for differences in language, education and cultural background without undermining their scientific validity?
The report argues for a more proportionate, evidence-based approach. Eligibility criteria should be reviewed throughout the development process, rather than treated as fixed rules. Greater flexibility may make recruitment easier, but its more important benefit is producing evidence that is relevant to a broader population. Inclusion and safety should not be seen as opposing objectives.
With two disease-modifying Alzheimer’s treatments now on the market, how is that affecting trial recruitment and design? For example, are patients less willing to enroll in placebo-controlled studies when an approved option exists? Should new therapies increasingly be tested against existing treatments instead of placebo?
The arrival of [Biogen and Eisai’s Leqembi] and [Eli Lilly’s Kisunla] has fundamentally changed the landscape of Alzheimer’s research and has already had a big impact, judging by the trial participants I spoke to for the report.
For patients and families, the prospect of receiving an active treatment can make participation in a study more attractive. Equally, where an approved treatment is available, and someone is eligible for it, the possibility of being allocated to a placebo group may be less appealing. That is a reasonable concern, particularly for people who feel they have limited time in which to benefit from treatment. Placebo-controlled trials remain important, but where there is an effective standard of care, investigators need to consider whether withholding an established treatment is ethically justified and whether an add-on design would be more appropriate. This is exactly what participants themselves are now asking.
As the Alzheimer’s treatment pipeline grows, which changes in trial design, recruitment strategies or international collaboration will be most important to help studies enroll and finish on time?
The first priority is to stop treating recruitment as something that begins once a trial protocol has been finalized. Recruitment needs to be built into the design from the outset, with patients, families and clinicians involved in identifying the barriers that might prevent people from taking part or staying in a study.
Better diagnostics could make a substantial difference. Blood-based biomarkers offer the potential to identify people with Alzheimer’s pathology more easily and, in some settings, reduce reliance on more expensive and invasive tests. Community-based screening and stronger links between primary care, memory services and research centers could also help identify potential participants earlier.
We should make participation less burdensome wherever possible. That might mean fewer unnecessary hospital visits, local assessments, remote follow-up (telemedicine) or carefully designed decentralized trials. These approaches need to preserve data quality and participant safety, but there is considerable scope to make research more practical for people with dementia and their caregivers.
International collaboration is equally important. Research remains concentrated in countries with established infrastructure, such as the U.S., U.K. and Japan, while many lower-income countries have limited access to trials despite the growing global burden of dementia. Building local diagnostic capacity, training researchers, and harmonizing regulatory processes could expand participation and accelerate recruitment.
Ultimately, speed should not be achieved at the expense of diversity. A trial that recruits quickly but excludes important groups may leave difficult questions unanswered. The goal is to recruit efficiently, retain participants, and produce results that are meaningful across different populations and health systems.
What should pharma companies take away from the report’s findings when planning future Alzheimer’s clinical development programs?
That a promising treatment cannot deliver its full potential if trials are too difficult to recruit for, exclude large sections of the population or generate evidence that is difficult to apply in everyday clinical practice.
Companies need to consider recruitment, diversity, participant burden and access at the earliest stages of development. That means designing protocols around the realities of living with dementia, engaging people with lived experience and their caregivers and working with clinicians and patient organizations to build trust. It also means investing in countries and communities that have historically been underrepresented in research.
There is a strong scientific argument for doing this well. More representative trials can provide a better understanding of how treatments perform across different populations, including people with other health conditions who are routinely encountered in clinical practice.
The industry should also recognize that Alzheimer’s is unlikely to be solved by a single treatment targeting a single mechanism. As the pipeline grows, there will be an increasing need to explore different approaches, combination therapies and treatments for people at different stages of the disease.
The opportunity is enormous, but innovation must be matched by rigorous evidence and a realistic understanding of how treatments will be used. Ultimately, success is not simply getting a drug through a trial or onto the market. It is developing treatments that make a meaningful difference to people’s lives, and ensuring that those who could benefit have a fair opportunity to access them.
