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Researchers analyzed more than 50,000 browser queries in Germany.
Google’s AI Overviews feature most often cites YouTube when answering health-related queries, according to a study by SE Ranking, which analyzed more than 50,000 searches in Germany. As reported by the Guardian, the findings have raised concerns about the reliability of a tool used by around 2 billion people each month.
Google says its AI Overviews are “reliable” and draw on authoritative sources such as the US Centers for Disease Control and Prevention and the Mayo Clinic. However, the study found that YouTube was the most frequently cited domain, with 20,621 references out of a total of 465,823 citations across 50,807 health-related queries and keywords. Overall, YouTube accounted for 4.43% of all citations in AI Overviews. No medical website, hospital network, government portal, or academic institution came close to this figure. Researchers emphasized that YouTube is a general-purpose platform rather than a specialized medical publisher.
“This matters because YouTube is not a medical content publisher,” the study’s authors said, noting that while some content is produced by doctors and clinics, the platform also hosts videos from influencers or creators without medical training.
The second most frequently cited source was the website of German public broadcaster NDR.de, with 14,158 citations, followed by Msdmanuals.com (9,711), health portal Netdoktor.de (7,519), and the medical career platform Praktischarzt.de (7,145).
In a statement to the Guardian, Google said AI Overviews are designed to surface high-quality content regardless of format. The company also noted that a significant share of YouTube content is produced by authoritative health organizations and licensed medical professionals.
“Claims that AI Overviews provide unreliable information are contradicted by the report’s own data, which shows that the most frequently cited domains are authoritative websites. Based on what we have seen in the published results, AI Overviews cite expert YouTube content from hospitals and clinics,” a Google spokesperson said.
Google also stated that 96% of the 25 most frequently cited YouTube videos came from medical channels. However, researchers pointed out that these videos represent less than 1% of all YouTube links cited in AI Overviews.
“At first glance, this looks quite reassuring. But it is important to remember that these 25 videos are only a tiny fraction of all YouTube links actually cited by AI Overviews. The situation with the remaining videos could be very different,” the authors said.
According to Hanna van Kolfschooten, a researcher in AI, health, and law at the University of Basel, the reliance on YouTube suggests that popularity, rather than medical reliability, is becoming the determining factor. She added that it is becoming increasingly difficult for Google to explain such results as isolated errors.
“This study provides empirical evidence that the risks associated with AI Overviews are structural rather than anecdotal,” van Kolfschooten said.
SE Ranking researchers acknowledged the limitations of their analysis, noting that it was a one-time data snapshot from December 2025 and focused only on Germany. Nevertheless, they stressed that the strong reliance on non-medical sources even within a tightly regulated healthcare system points to a potentially broader problem extending beyond a single country.
