Yes, prevention trials are increasingly targeting preclinical Alzheimer’s disease—people who show brain changes consistent with Alzheimer’s pathology but have no cognitive symptoms yet. Several large studies are already underway, including the Amyloid Biomarker Study (ABS), which enrolls cognitively normal individuals with elevated amyloid levels detected through PET imaging or cerebrospinal fluid tests. These trials represent a fundamental shift in how researchers approach Alzheimer’s: rather than waiting for memory loss to appear, they’re testing whether drug intervention in the asymptomatic stage can prevent or delay cognitive decline.
The rationale is straightforward. By the time someone notices memory problems, significant neurodegeneration has already occurred—a window that may be too late for some interventions. People in the preclinical stage, identified through biomarkers, may still have a viable opportunity for prevention. However, this approach raises complex questions about whom to treat, how to identify candidates reliably, and whether preventing pathology actually prevents symptoms.
Table of Contents
- Why Preclinical Alzheimer’s Is the Target for Prevention Studies
- How Prevention Trials Identify Preclinical Participants
- Drugs and Mechanisms Tested in Preclinical Prevention Trials
- Who Can Participate—Practical Eligibility and Screening
- Safety Concerns Specific to Preclinical Populations
- What Early Prevention Trial Results Teach
- Future Direction and Ongoing Recruitment Efforts
Why Preclinical Alzheimer’s Is the Target for Prevention Studies
Alzheimer’s disease unfolds in stages that researchers have come to understand only in the past 15 years. Amyloid-beta and tau proteins begin accumulating in the brain years—sometimes decades—before cognitive symptoms appear. Autopsy studies and imaging research have shown that many cognitively normal older adults have substantial brain pathology at death, suggesting the disease progresses silently for extended periods. This preclinical window is what prevention trials are designed to capture. The logic of early intervention mirrors cancer screening: detecting a disease process before it causes clinical harm offers the best chance to stop it.
A person with elevated amyloid but normal cognition has not yet experienced widespread neurodegeneration or neuroinflammation that might be irreversible. If an anti-amyloid drug can clear or stabilize amyloid levels during this window, the theory goes, it might prevent the cascade of tau tangles, neuronal loss, and cognitive decline. The A4 Study, which recruited cognitively normal people with amyloid positivity, follows this exact model. One limitation worth noting: most people with amyloid pathology never develop cognitive impairment. Some live into advanced age with abundant amyloid in the brain and die with normal cognition intact. This means prevention trials inevitably treat many people who would never have progressed to symptomatic disease, raising questions about benefit-to-harm ratios and the long-term effects of preventive drugs in cognitively normal populations.
How Prevention Trials Identify Preclinical Participants
Prevention trials locate preclinical Alzheimer’s using biomarkers—objective measures of brain pathology that don’t rely on cognitive testing. The most commonly used markers are amyloid-beta and phosphorylated tau, detected through positron emission tomography (PET) brain imaging or cerebrospinal fluid sampling. Some trials now use blood biomarkers, including phosphorylated tau variants (p-tau181, p-tau217) and plasma phospho-tau/amyloid ratios, which are faster and cheaper to measure than imaging but require validation in diverse populations. A critical warning: biomarker positivity is not diagnosis. A person can have amyloid and tau abnormalities and never develop cognitive symptoms. Blood biomarkers, though easier to access, are still evolving, and their predictive accuracy varies significantly across age groups and ancestries.
Many trials have under-enrolled Black and Hispanic participants, meaning the predictive value of biomarkers in these populations remains poorly understood. This creates a two-tier risk: treating people unnecessarily, and potentially missing those who would benefit because the biomarker isn’t validated in their demographic. The identification process itself is also a barrier. PET imaging requires specialized centers and is expensive; cerebrospinal fluid requires a lumbar puncture, an invasive procedure some people decline. Blood biomarkers reduce this friction, but they’re not yet standard in primary care. As a result, most preclinical trial participants are identified through research screening or referred from memory clinics—populations that may differ from the general aging population they’re meant to represent.
Drugs and Mechanisms Tested in Preclinical Prevention Trials
The first monoclonal antibodies targeting amyloid—aducanumab, lecanemab—were tested partly through recruitment of preclinical populations. Lecanemab showed modest slowing of cognitive decline in people with mild cognitive impairment and amyloid pathology (the Clarity AD trial), and based on this, the preventive A4 Study tested whether earlier intervention in cognitively normal amyloid-positive people could prevent progression. The trial, published in 2024, found that lecanemab did reduce amyloid in the brain but showed no clear benefit on cognitive decline over three years—raising questions about whether clearing amyloid alone, in asymptomatic people, translates to cognitive protection. Several other trials are testing different mechanisms. Anti-tau drugs, immunotherapy approaches, and anti-inflammatory agents are being evaluated in preclinical cohorts.
The Dominantly Inherited Alzheimer Network (DIAN) Prevention Trial tests solanezumab in cognitively normal members of families with early-onset Alzheimer’s mutations—a higher-risk preclinical population than community-based screenings. This population design makes sense because mutation carriers have near-certain disease progression, unlike biomarker-positive individuals drawn from the general population who may never progress. A practical tradeoff exists between recruitment speed and scientific rigor. Screening thousands of cognitively normal people to find biomarker-positive candidates is expensive and time-consuming. Family-based trials in mutation carriers recruit faster and have higher progression rates, but results may not generalize to sporadic Alzheimer’s (the 99% of cases without a known genetic cause). Many prevention trials try to balance both approaches, but this dual strategy stretches budgets and recruitment timelines.
Who Can Participate—Practical Eligibility and Screening
Prevention trial eligibility typically requires being cognitively normal, meaning normal performance on cognitive testing, normal function in daily life, and no subjective cognitive complaints (or only mild ones). Age requirements usually start at 55 or 60, though some trials accept younger adults at high genetic risk. Biomarker positivity is essential—either amyloid, tau, or both—though the specific threshold varies. Some trials require only amyloid; others require both amyloid and neurodegeneration (evidence of brain atrophy on MRI); and some now use blood biomarkers as the entry criterion. Medical contraindications exist. Participants usually must be on stable medications and have no active cancer, psychiatric disease, or neurological conditions other than preclinical Alzheimer’s.
Pregnancy precludes enrollment because the long-term effects of anti-amyloid antibodies in pregnancy are unknown. Kidney disease can affect drug clearance and is often an exclusion. These restrictions mean that participants in prevention trials are typically relatively healthy, well-educated, and well-connected to medical care—a population that may not represent the diversity of people who develop Alzheimer’s in the real world. One practical consideration: participating in a prevention trial often requires repeated visits (sometimes monthly), imaging scans (PET or MRI), blood draws, and cognitive testing. This commitment lasts years. Dropout rates vary but can be 20–30% over multiyear studies. People with transportation challenges, inflexible work schedules, or limited access to trial sites are less likely to enroll or complete, introducing selection bias into who benefits from trial-tested drugs.
Safety Concerns Specific to Preclinical Populations
Anti-amyloid monoclonal antibodies carry a known safety risk called amyloid-related imaging abnormalities (ARIA)—microhemorrhages and microinfarcts detected on MRI that can occur even in asymptomatic people. In the A4 trial, ARIA was more common in people taking lecanemab than placebo, though most events were subclinical (no symptoms). However, the long-term consequence of asymptomatic microhemorrhages is unknown. In a cognitively normal person, discovering an asymptomatic brain lesion raises ethical questions: Should they be told? Could knowledge of the lesion cause psychological harm? What if the lesion becomes symptomatic years later? Another concern is that preclinical trials test drugs for years in people who may never have developed symptoms anyway.
If a trial shows that a drug slows amyloid accumulation but does not prevent cognitive decline—as the A4 study suggested—participants have spent years receiving an intervention with unclear long-term benefit and unknown decades-long safety profile. The benefit-to-harm ratio becomes difficult to assess when the harm may take 10 or 20 years to materialize and the benefit is prevented symptom onset that might never have occurred. There is also a risk of creating a new category of disease: asymptomatic people labeled as having “preclinical Alzheimer’s” based on a biomarker, requiring them to take drugs indefinitely. This medicalization could affect insurance coverage, employment, or psychological well-being, particularly if the biomarker-positive prediction later proves unreliable in diverse populations or if people remain cognitively normal into advanced age.
What Early Prevention Trial Results Teach
The A4 Study’s 2024 findings—that lecanemab reduced amyloid burden but not cognitive decline in cognitively normal amyloid-positive people—suggest that amyloid clearance alone may not be sufficient. This contrasts with findings in people who already have mild cognitive impairment (Clarity AD), where lecanemab showed modest slowing of decline. One interpretation is that amyloid alone, without significant tau or neurodegeneration, is less predictive of future cognitive loss. Another is that the cognitive benefit only becomes apparent over longer follow-up than the 3–4 years most trials track.
A third possibility is that the benefit exists but is small enough to be missed, or that it only emerges in subgroups (those with very high amyloid or specific biomarker profiles). The DIAN Prevention Trial, which tested a different anti-amyloid drug in autosomal dominant Alzheimer’s mutation carriers, also showed amyloid reduction without clear cognitive benefit, though follow-up data are still emerging. These results have tempered expectations that prevention is simply earlier treatment. They’ve redirected research interest toward multi-target approaches—simultaneously addressing amyloid, tau, neuroinflammation, and metabolic dysfunction—rather than monotherapy.
Future Direction and Ongoing Recruitment Efforts
New prevention trials are launching with modified designs based on A4 results. Some focus on people with both amyloid and tau abnormalities, on the theory that dual pathology is more predictive of decline than amyloid alone. Others target specific populations at higher risk, such as those with a family history of Alzheimer’s or carriers of the APOE4 gene variant. A few are testing anti-inflammatory or metabolic interventions in preclinical cohorts, moving beyond amyloid-focused approaches.
The Amyloid Biomarker Study and related cohorts continue to enroll and follow participants, collecting decades of longitudinal data that will ultimately determine whether preclinical identification and treatment can meaningfully change disease trajectory. For now, prevention trials do exist and actively recruit cognitively normal amyloid-positive individuals, but the evidence for their efficacy remains mixed. Participation offers access to advanced imaging and biomarker testing, close monitoring, and the possibility of receiving a potentially disease-modifying drug, though with the caveat that benefit in preclinical stages has not yet been demonstrated. The field is learning, in real time, whether targeting Alzheimer’s before symptoms appear is a viable approach or whether the disease requires more advanced pathology to respond to intervention.
