Why does PubMed Central top the health ranking?

PubMed Central is the free biomedical archive run by the US National Institutes of Health, so it holds the raw peer-reviewed research the models treat as the most authoritative answer to a medical question. In our July 2026 study it was the single most-cited health source, with 33,669 citations, ahead of YouTube, Google and Reddit.

Which AI engine cites Reddit and YouTube most for health?

Google's search AI does. In the founding study, Google AI Overviews and AI Mode cited social and user-generated content four to five times more than ChatGPT (8.5% and 7.6% versus 1.9%). ChatGPT was the most authority-first engine and almost never cited Reddit or YouTube for health.

Why do the famous health brands rank so low?

They are cited, just not heavily. Mayo Clinic, WebMD, Healthline and Cleveland Clinic each held well under 1% of health citations individually. Only 17.3% of all health citations went to authoritative medical sources, and the rest spread across a long tail of commercial sites, apps and platforms.

How is this ranking built?

This is a cohort ranking of every domain cited in answers to non-branded US health questions tracked for healthcare brands, not a curated list. Domains that appear in only a narrow slice of those question sets are dropped so no single one can dominate the ranking.

How often is this ranking updated?

The ranking is rebuilt daily over a 28-day rolling window. The snapshot date in the hero shows the last refresh.

Google AI Overviews · Top US Health Sources cited by AI

US health sources cited most by Google AI Overviews

The domains Google AI Overviews cite most for US health questions. 28-day rolling window.

Updated Aug 8, 2026

US health source citation share: last 90 days

Stacked 100%

Share of US health answers that cite each domain. 28-day rolling window.

Top US health sources cited by AI

Share is the percentage of US health answers in the 28-day window that cited at least one link on each domain.

Rank	Source domain	Value
1	youtube.com	40.07%
2	nih.gov	21.35%
3	reddit.com	11.37%
4	sciencedirect.com	8.53%
5	google.com	7.7%
6	facebook.com	7.34%
7	instagram.com	6.66%
8	healthline.com	5.93%
9	linkedin.com	5.79%
10	clevelandclinic.org	5.02%

Want this data for your own brand? See the Google AI Overviews visibility tracker

What this report covers

In our July 2026 study of roughly 825,000 citations to non-branded US health questions, peer-reviewed research sat at the top. PubMed Central was the single most-cited domain, ahead of YouTube, Google and Reddit. This page keeps that ranking live on the LLM Pulse dataset.

The split between engines is the story. ChatGPT trusts medical and academic authority most, while Google's search AI cites Reddit and YouTube far more often, so the per-model pages above look very different from one another. The ranking is rebuilt daily over a 28-day window.

How we measure this

LLM Pulse tracks every citation in every answer across ChatGPT, Perplexity, Gemini, Google AI Mode and Google AI Overviews.
This report keeps citations shown to US users on non-branded health questions tracked for healthcare brands, then ranks the domains cited. Answers pointing to a tracked brand's own domain are excluded.
A domain counts once per answer, and domains that appear in only a narrow slice of question sets are dropped. 28-day rolling window, rebuilt daily.

Why this matters

Health is the category where accuracy carries real stakes, so where AI reaches for its answers matters. This ranking shows the mix, with research archives and government sites near the top and social platforms far larger than most people expect.

For any brand in health, wellness or care, visibility is won at the level of individual pages and studies, not domain authority alone. LLM Pulse tracks which of your pages the models cite and how that changes over time.

Frequently Asked Questions

: PubMed Central is the free biomedical archive run by the US National Institutes of Health, so it holds the raw peer-reviewed research the models treat as the most authoritative answer to a medical question. In our July 2026 study it was the single most-cited health source, with 33,669 citations, ahead of YouTube, Google and Reddit.
: Google's search AI does. In the founding study, Google AI Overviews and AI Mode cited social and user-generated content four to five times more than ChatGPT (8.5% and 7.6% versus 1.9%). ChatGPT was the most authority-first engine and almost never cited Reddit or YouTube for health.
: They are cited, just not heavily. Mayo Clinic, WebMD, Healthline and Cleveland Clinic each held well under 1% of health citations individually. Only 17.3% of all health citations went to authoritative medical sources, and the rest spread across a long tail of commercial sites, apps and platforms.
: This is a cohort ranking of every domain cited in answers to non-branded US health questions tracked for healthcare brands, not a curated list. Domains that appear in only a narrow slice of those question sets are dropped so no single one can dominate the ranking.
: The ranking is rebuilt daily over a 28-day rolling window. The snapshot date in the hero shows the last refresh.

The industry's leading AI citation dataset, pointed at your brand

This page is the public tip of the LLM Pulse iceberg. Internally we track millions of AI answers every week across every major AI search engine, rolled up to the citation, the brand mention and the sentiment level. Point it at your own domain in under a minute.

Roughly 825,000 US health citations analyzed in the founding study
Five AI search engines tracked: ChatGPT, Perplexity, Gemini, AI Mode, AI Overviews
Every domain the models cite, ranked by breadth across health topics

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