Gemini gives no source at all in 77.1% of its answers to health questions, against 2.4% for ChatGPT. When AI answers do cite, the National Institutes of Health dominates: nih.gov appears in 32.3% of sourced health answers, three times the rate of the next website, the CDC.
Analysis of 1,600 AI answers to 400 health questions · ChatGPT and Gemini, September 2026
Key Findings
- 1.Gemini answers 77.1% of health questions without citing any source, against 2.4% for ChatGPT.
- 2.nih.gov is the most-cited website in AI answers to health questions, appearing in 32.3% of ChatGPT and Gemini answers that cite a source, three times the CDC's 10.6%.
- 3.ChatGPT cites nih.gov in 38.3% of its sourced health answers; Gemini's top health source is Wikipedia, at 14.8%.
- 4.Government and university websites take 36.2% of the citations in AI answers to health questions, the third-highest share of 12 industries.
- 5.Forums, social media, video and other user-generated sites take 0.6% of the citations in AI answers to health questions.
Summary
A parent asks an AI assistant whether a child's fever needs a doctor. On ChatGPT, the answer nearly always points to its evidence, most often the National Institutes of Health or the CDC. On Gemini, three answers in four come with no source at all, so the parent cannot see where the advice came from or check it.
Health is where sources matter most, to readers and to the businesses that publish health information. A citation is the link an AI answer shows as its evidence. For a clinic, a health brand or a health publisher, the cited websites are the competition, and the engines' habits decide how many citations there are to win.
Gemini cites no source in 77.1% of health answers, against 2.4% for ChatGPT. When AI answers do cite, government sources lead by a wide margin: nih.gov appears in 32.3% of sourced answers, followed by the CDC at 10.6% and Cleveland Clinic at 7.7%, and government and university websites take 36.2% of all health citations.
What we measured
On September 23, 2026 we asked ChatGPT and Gemini 400 health questions, each twice, as part of a wider study of AI sources across 12 industries. That gave 1,600 answers, 964 of which cited at least one source. Across them, AI cited 760 different websites.
A website's share is the percentage of sourced answers that cite it at least once, counting all pages from the same site together, so every NIH institute counts as nih.gov. We also sorted every citation by the kind of website behind it: government and education (.gov, .edu and .mil addresses), nonprofits and associations (.org), media and reference publishers, user-generated sites such as forums, social media and video platforms, and companies and other commercial websites.
NIH leads by a wide margin
No other website comes close. The CDC is second at 10.6%, then Cleveland Clinic (7.7%), the FDA (7.1%) and the UK's NHS (5.3%). The World Health Organization, MedlinePlus, the Sleep Foundation and Wikipedia follow, and Mayo Clinic ranks 10th at 4.1%. Government sources fill much of the list: NIH, CDC, FDA, MedlinePlus, cancer.gov and HHS all sit in the top 25.
Source: Suff Digital analysis of 1,600 AI answers to 400 health questions · ChatGPT and Gemini, September 2026
| Rank | Website | All answers | ChatGPT | Gemini |
|---|---|---|---|---|
| 1 | nih.gov | 32.3% | 38.3% | 6.6% |
| 2 | cdc.gov | 10.6% | 12.4% | 2.7% |
| 3 | clevelandclinic.org | 7.7% | 7.3% | 9.3% |
| 4 | fda.gov | 7.1% | 8.7% | 0% |
| 5 | nhs.uk | 5.3% | 6.1% | 1.6% |
| 6 | who.int | 5.2% | 6.3% | 0.5% |
| 7 | medlineplus.gov | 5% | 6.1% | 0% |
| 8 | sleepfoundation.org | 4.9% | 4.4% | 7.1% |
| 9 | wikipedia.org | 4.5% | 2% | 14.8% |
| 10 | mayoclinic.org | 4.1% | 4.6% | 2.2% |
| 11 | cancer.gov | 3.4% | 4.2% | 0% |
| 12 | healthline.com | 3% | 1.3% | 10.4% |
| 13 | healthychildren.org | 2.8% | 3.5% | 0% |
| 14 | openstax.org | 2.4% | 2.9% | 0% |
| 15 | medicalnewstoday.com | 2.3% | 0.8% | 8.7% |
Cleveland Clinic is the one website in the top five that both engines cite often: 7.3% of ChatGPT's sourced answers and 9.3% of Gemini's.
Gemini rarely shows its sources on health
ChatGPT cites a source in 97.6% of its health answers, listing 2.3 websites on average. Gemini cites a source in 22.9%, though when it does, it lists 3.8 websites. Across both engines, 39.8% of health answers cite nothing, almost all of them from Gemini.
Source: Suff Digital analysis of 1,600 AI answers to 400 health questions · ChatGPT and Gemini, September 2026
| Measure | ChatGPT | Gemini |
|---|---|---|
| Answers with no source | 2.4% | 77.1% |
| Websites per sourced answer | 2.3 | 3.8 |
| Most-cited website | nih.gov | wikipedia.org |
| Share of sourced answers citing it | 38.3% | 14.8% |
The two engines also cite different websites. ChatGPT leans on government: nih.gov in 38.3% of its sourced answers, the CDC in 12.4% and the FDA in 8.7%. Gemini's sourced answers favor Wikipedia (14.8%), Healthline (10.4%), Cleveland Clinic (9.3%) and Medical News Today (8.7%); apart from Cleveland Clinic, ChatGPT cites these publishers far less. A health publisher can be well placed on Gemini and nearly invisible on ChatGPT, or the reverse.
How health compares with other industries
Government and university websites take 36.2% of health citations and companies and other commercial websites 33.6%. That official share ranks 3rd of 12 industries, behind fitness (45.5%) and home improvement (39.2%). User-generated content takes 0.6% of health citations, next to nothing, against 3.8% in legal.
Source: Suff Digital analysis of 1,600 AI answers to 400 health questions · ChatGPT and Gemini, September 2026
| Industry | Top source | Share of sourced answers | Government and university share | User-generated share |
|---|---|---|---|---|
| Health | nih.gov | 32.3% | 36.2% | 0.6% |
| Fitness | nih.gov | 41.5% | 45.5% | 0.2% |
| Recipes | usda.gov | 37.5% | 31.8% | 2.1% |
| Real estate | consumerfinance.gov | 27.2% | 26.9% | 1.6% |
| Software | apple.com | 24.3% | 4.7% | 3.2% |
| Pets | vcahospitals.com | 18.4% | 10.1% | 3.1% |
| Legal | americanbar.org | 14.7% | 20.6% | 3.8% |
| Money | irs.gov | 13.8% | 30.2% | 1.7% |
| Travel | delta.com | 13.2% | 8.1% | 2.8% |
| College | consumerfinance.gov | 13.1% | 32.1% | 2.1% |
| Home improvement | energy.gov | 11.8% | 39.2% | 1.6% |
| Cars | consumerreports.org | 6.7% | 11.4% | 2.9% |
Health is also one of the most concentrated industries. Its top source, nih.gov, reaches 32.3% of sourced answers, a share beaten only by nih.gov in fitness (41.5%) and usda.gov in recipes (37.5%). On health and fitness questions, a single government website sets much of the evidence AI answers rest on.
What this means for health brands and publishers
On health questions, AI engines, and ChatGPT in particular, defer to government and academic sources, so a commercial health site is cited alongside NIH and the CDC. The way in is to cite those sources, match their guidance and add practical detail for your patients: plain-language explanations, costs and local information. Pages written by named clinicians, with clear dates and references, give AI engines the evidence they look for.
Gemini needs a different plan. It gives no source in 77.1% of health answers, and when it does cite, it favors Wikipedia and health publishers such as Healthline and Cleveland Clinic. Being named and described accurately in the text of its answers matters as much as the link. Our healthcare seo team builds health content that AI engines can find, trust and cite.
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Cite this study
Suff Digital. (2026). Gemini Answers 77.1% of Health Questions Without Citing a Source vs 2.4% for ChatGPT. https://www.suffdigital.com/resources/data-studies/ai-sources-health-questions
Gemini Answers 77.1% of Health Questions Without Citing a Source vs 2.4% for ChatGPT - Suff Digital - https://www.suffdigital.com/resources/data-studies/ai-sources-health-questions
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