Why is Alzheimer's disease so difficult to treat?

Prevalence of Alzheimer's disease

Alzheimer’s disease is a neurodegenerative disorder in which nerve cells in the brain progressively die, resulting in development of dementia that negatively affects memory and cognitive behavior. The symptoms such as memory loss, disorientations, and mood/behavior changes eventually grow severe enough to interfere with daily routines.

According to the Alzheimer's Association, over 7 million Americans are currently living with Alzheimer’s disease, and by 2050, the number is projected to increase to nearly 13 million. Among American population age 65 and older, about 1 in 9 people has Alzheimer’s. The long-term health care cost burden for people living with dementia is projected to reach about $384 billion in 2025 and nearly $1 trillion in 2050.

Pathology of Alzheimer’s disease

Alzheimer’s disease is known for two primary neuropathology: 1) extracellular amyloid-β plaques, and 2) intraneuronal Tau neurofibrillary tangles (NFTs). Accumulation of these protein aggregates ultimately leads to brain cell dysfunction and loss, which are associated with cognitive decline.   

Why is Alzheimer’s disease so difficult to treat?

Despite decades of research, the FDA-approved treatment options for Alzheimer’s disease are still limited. Currently, there are two FDA-approved drugs in the market that directly targets to reduce amyloid- β plaques in the brain to treat people living with Alzheimer’s disease. One is Lecanemab (Lequmbi), which is a monoclonal antibody that reduces amyloid- β plaques and modestly slows cognitive decline in people with early Alzheimer’s and mild cognitive impairment. The other is Donanemab (Kinsula), another antibody targeting amyloid- β plaques for treating mild cognitive impairment and mild dementia.

Benefits and risk of the current treatment?

Although the existence of these two FDA-approved drugs for treatment of Alzheimer’s is an impressive accomplishment, their benefits are still considered modest at best. Additionally, administration of Lecanemab and Donanemab do not come without risks. Both treatments carry significant risks of Amyloid-Related Imaging Abnormalities (ARIA), which refer to brain swelling and hemorrhages visible on MRI. Some of the symptoms of ARIA include headache, cognitive worsening, seizures, and visual changes.

Hypotheses on amyloid-β plaques

When it comes to hypothesis regarding the pathology of Alzheimer’s disease, there are two schools of thought. 1) amyloid-β plaques are the driving cause of Alzheimer’s disease vs. 2) amyloid-β plaques are merely a byproduct of another factor that is upstream of amyloid-β plaques formation that might be actually causing Alzheimer’s disease. The second hypothesis stems from the scholars recognizing the lack of successful treatment for the disease despite the decades of research built upon the first hypothesis.

Physiology vs. Pharmacology, Cure vs. Treatment,

The concept of Physiology vs. Pharmacology refers to the question of cure vs. treatment: does the drug pharmacologically treat the disease, or does it fix physiology and therefore cure the disease?

Developing treatments for Alzheimer’s disease is increasingly converging with efforts to target the biology of aging itself because aging and Alzheimer’s share multiple cellular and molecular hallmarks, including impaired proteostasis, mitochondrial dysfunction, chronic low-grade inflammation, and reduced stress resistance. These aging processes promote accumulation of misfolded proteins (Aβ, tau), synaptic dysfunction, vascular injury, and vulnerability of neurons and glia, which collectively create a permissive environment for Alzheimer’s pathology.​ Since many believe that age is the dominant risk factor and many core hallmarks of aging directly drive Alzheimer pathology and progression, there is growing interest in therapeutic methods that might simultaneously slow the natural aging processes and reduce Alzheimer risk.

The question for the drug developers working in therapeutic area like dementia and Alzheimer’s disease is “does a developed drug slow down the progression of the disease by targeting amyloid- β plaques and/or P-tau aggregates” or “does it slow down the progression of the disease by slowing down the aging mechanism in general?”

Shared biology of Alzheimer’s disease and aging

Aging and Alzheimer’s share multiple cellular and molecular hallmarks, including impaired proteostasis, mitochondrial dysfunction, chronic low-grade inflammation, and reduced stress resistance. These aging processes promote accumulation of misfolded proteins (Aβ, tau), synaptic dysfunction, vascular injury, and vulnerability of neurons and glia, which collectively create a permissive environment for Alzheimer’s pathology.​ Chronological age is the strongest non-modifiable risk factor for developing Alzheimer’s, and epidemiologic data show incidence rising steeply with each decade after midlife. Even in cognitively normal older adults, aging is associated with progressive amyloid and tau deposition, brain atrophy, and cognitive slowing, suggesting that Alzheimer represents a maladaptive extension or acceleration of brain aging.​

Alzheimer’s as accelerated or maladaptive aging

Several lines of work indicate that people along the Alzheimer continuum show “biologically older” signatures than age-matched controls, such as accelerated inflammatory proteome aging, epigenetic age acceleration, and older-appearing brains on imaging-based “brain-age” models. These data support the view that Alzheimer’s can be conceptualized, at least partly, as a state of accelerated or dysregulated aging in specific brain circuits and cell populations.​

Geroscience approach to Alzheimer therapeutics

The geroscience framework proposes that targeting upstream aging mechanisms could delay or prevent multiple age-related diseases, including Alzheimer’s, rather than focusing solely on downstream disease-specific lesions. In this context, interventions like senolytics, rapalogues, caloric-restriction mimetics, autophagy enhancers, and mitochondrial or vascular-targeted therapies are being explored as ways to broadly improve brain resilience and potentially slow Alzheimer progression.​

Future Direction?

Because aging processes are shared across tissues and diseases, drugs that modulate aging biology might yield pleiotropic benefits but also raise new safety, trial-design, and regulatory challenges, especially when used preventively in at-risk but asymptomatic older adults. Integrating geroscience into Alzheimer drug development means designing trials that use aging biomarkers (epigenetic clocks, inflammatory age, brain age) as stratifiers or endpoints and combining disease-specific agents (e.g., anti-amyloid, anti-tau) with upstream aging-targeted interventions.

Another effort to help people who may develop Alzheimer’s disease is finding practical and accessible methods for early detection of the progression of the disease. Blood test for early detection of Alzheimer’s disease is possible by measuring the plasma Aβ composite biomarkers such as Aβ₄₂ and Aβ₄₀ , which are correlated with a decline in memory. Early detection would allow people to consider treatment options before the symptoms progress further.

Additionally, a significant fraction of Alzheimer’s disease is facilitated by lifestyle components such as stress, sleep deprivation, diet, and insufficient physical activity. For example, a chronic physical and/or emotional stress increases glucocorticoid secretion by the adrenal cortex, which leads to elevation of both Aβ deposition and P-tau levels in the brain, neuronal atrophy, and inhibition of neurogenesis, thereby contributing to Alzheimer’s disease. A strategic lifestyle adjustment will be important for people, as we are projected to live longer.

References

1. Alzheimer’s Association. Alzheimer’s Disease Facts and Figures. Alzheimer’s Association. Published [year unknown]. Accessed February 16, 2026. https://www.alz.org/alzheimers-dementia/facts-figures 

2. Selkoe DJ, Lansbury PJ Jr. Alzheimer’s Disease Is the Most Common Neurodegenerative Disorder. In: Basic Neurochemistry. National Center for Biotechnology Information (US). Accessed February 16, 2026. https://www.ncbi.nlm.nih.gov/books/NBK27944/ 

3. Selkoe DJ, Hardy J. The amyloid hypothesis of Alzheimer’s disease at 25 years. EMBO Mol Med. 2016;8(6):595-608. doi:10.15252/emmm.201606210. PubMed Central PMCID: PMC4888851. Accessed February 16, 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC4888851/

4. Mayo Clinic Staff. Alzheimer’s: Medicines help manage symptoms and slow decline. Mayo Clinic. Accessed February 16, 2026. https://www.mayoclinic.org/diseases-conditions/alzheimers-disease/in-depth/alzheimers/art-20048103

Assessed and Endorsed by the MedReport Medical Review Board