Research

Letters, spotlights, and commentary.

A weekly Warning Letter analysis on Monday. A named-brand audit on Wednesday. A Friday read of the Index. Open and footnoted. Published by EvidenceSignal Research.

Filter All Letters of the Week Brand Spotlights Commentary
Friday Commentary May 25, 2026 5 min

What Moved the Index: Sleep Gummies Are Eating Sleep Pills

Sleep gummies hold the top AI recommendation across all four major engines.

Letter of the Week May 25, 2026 5 min

The Warning Letter That Quietly Rewrote Immunity Claims

How an FDA Warning Letter changed the way AI engines handle immunity claims.

Friday Commentary May 25, 2026 4 min

Six Weeks After the March NAD Cohort

Eight supplement brands received NAD decisions in March 2026.

Brand Spotlight May 25, 2026 4 min

Childrens Multivitamins and the Language AI Engines Wont Say

AI engines systematically soften children supplement claims. A composite case study.

Brand Spotlight May 25, 2026 5 min

How Iron Rock NAD+ Captured 14% of AI Citation Share in 90 Days

Analysis of how a supplement brand white-paper strategy drove AI citation share.

Brand Spotlight May 25, 2026 5 min

The Liposomal Bioavailability Problem

Liposomal supplements claiming high absorption without NAD substantiation.

Letter of the Week May 25, 2026 5 min

EU Natural: Migration Away from Disease Language

14 months of copy revisions after a 2021 FDA Warning Letter.

Letter of the Week May 25, 2026 5 min

Thang Botanicals 7-OH: When Kratom Becomes a CGMP Case

FDA Warning Letter signals manufacturing enforcement shift for kratom.

Friday Commentary May 25, 2026 5 min

Why AG1 Leads on Perplexity but Trails on Claude

AG1 ranks first on Perplexity and third on Claude across greens-powder queries.

Letter of the Week May 24, 2026 1 min

Cape Fear Naturals and the twenty-one phrases that landed an FDA citation

A 2017 Warning Letter to a small North Carolina compounder cited 21 separate disease and structure-function claims across twelve products. Read carefully, it is a map of where the FDA draws the line — and a map most marketing teams have never seen.