What is the FDA accelerated approval pathway, and why does it matter for Alzheimer's?

What it is

Accelerated approval is one of the FDA's regulatory pathways for bringing a drug to market. It was created in 1992, originally to address the urgency of the HIV/AIDS epidemic, and has since been used across many disease areas - most often in oncology, increasingly in rare disease, and in a small number of high-profile cases in Alzheimer's.

Under the standard FDA approval pathway - sometimes called full or traditional approval - a drug must show a clinical benefit on a clinically meaningful endpoint in adequate and well-controlled trials before approval. Under accelerated approval, the drug can be approved earlier on the basis of either a surrogate endpoint or an intermediate clinical endpoint that is "reasonably likely to predict" the ultimate clinical benefit.

The trade-off is that the sponsor commits to running a confirmatory trial after approval to verify the predicted clinical benefit. If the confirmatory trial fails, or is not completed, the FDA has the authority to withdraw the approval.

How a surrogate endpoint differs from a clinical endpoint

A clinical endpoint is something a patient or their family would directly recognise: how long the patient lives, whether their symptoms improve, how their function changes. In Alzheimer's, CDR-SB and iADRS are clinical endpoints - they measure cognitive and functional impairment as it shows up clinically.

A surrogate endpoint is a biological measure that is expected to track with clinical benefit, even though it is not the clinical benefit itself. In Alzheimer's, the most prominent surrogate is amyloid clearance on amyloid PET - the idea is that removing amyloid from the brain should, if the underlying disease theory is correct, translate into preserved cognitive and functional ability over time.

Accelerated approval lets the FDA act on the surrogate evidence first, with the agreement that the clinical benefit will be confirmed afterwards. The pathway depends on a chain of reasoning: surrogate change is expected to track clinical change; the trial showed surrogate change; therefore the drug is reasonably likely to produce clinical benefit. If any link in that chain breaks, the case for the approval breaks with it.

Why it matters for Alzheimer's specifically

Alzheimer's has been the highest-profile recent test of accelerated approval in a non-oncology setting.

Aducanumab (Aduhelm). In 2021, aducanumab received accelerated approval based on amyloid clearance, despite mixed clinical-trial results and a near-unanimous advisory-committee vote against approval. The decision drew sustained criticism on scientific, regulatory, and ethical grounds. Confirmatory clinical evidence did not materialise in a way that resolved the questions raised at approval. The sponsor voluntarily withdrew the product from the market in 2024.

Lecanemab (Leqembi). Initially received accelerated approval in early 2023 on the basis of amyloid clearance, then converted to full traditional approval later that year on the basis of clinical-endpoint evidence from CLARITY-AD. The accelerated-to-full conversion is the pathway working as designed.

Donanemab (Kisunla). Received traditional approval in 2024 directly on clinical-endpoint evidence from TRAILBLAZER-ALZ 2, without going through accelerated approval first. This was a noticeable choice of route by the agency at the time.

The cumulative effect of these episodes is what our Signal on post-aducanumab accelerated-approval scrutiny tracks. The pathway still exists, and is still available to Alzheimer's sponsors. But the surrogate-evidence bar - particularly for a sponsor proposing accelerated approval on a new mechanism in this disease area - is meaningfully higher than it was three years ago.

What it can and cannot do

It can:

• Bring a drug to market earlier, on the basis of a well-justified surrogate, in a disease area where the unmet need is substantial.
• Generate the confirmatory clinical evidence in parallel with patient access, rather than gating one on the other.
• Be converted to a traditional approval if the confirmatory evidence supports it (as with lecanemab).
• Be withdrawn if the confirmatory evidence does not (as with aducanumab).

It cannot:

• Substitute for a sound surrogate endpoint. If the surrogate-to-clinical link is not well-supported, accelerated approval gives the field a drug whose clinical benefit is genuinely uncertain.
• Avoid the post-marketing scrutiny that comes with the pathway. CMS coverage frameworks like coverage with evidence development often follow accelerated approval and shape how the drug is actually delivered to patients.
• Resolve disagreements about meaningfulness. The interpretive questions about small absolute changes on cognitive and functional scales are independent of the regulatory route - they apply whether the approval is accelerated or traditional.

Why it keeps coming up

Accelerated approval is the regulatory lever the field reaches for when the clinical-endpoint evidence is taking longer than the unmet need can wait - but only when the surrogate evidence is strong enough to justify the bet. The bar has been recalibrated for Alzheimer's specifically, and that recalibration is one of the parameters anyone forecasting the next wave of submissions has to price in. For the broader regulatory context of where the field stands, see our regulatory landscape snapshot for 2026.

This page is a plain-language primer. It is not legal, regulatory, or medical advice.