Half of AI Health Advice Is Wrong—And Seems Just Right

In brief

• Nearly half of AI chatbot responses to health questions were rated "somewhat" or "highly" problematic in a BMJ Open audit of five major chatbots.
• Grok produced significantly more "highly problematic" responses than statistically expected, while nutrition and athletic performance questions fared worst across all models.
• No chatbot produced a fully accurate reference list.

Nearly half of the health and medical answers provided by today's most popular AI chatbots are wrong, misleading, or dangerously incomplete—and they're delivered with total confidence. That's the headline finding of a new peer-reviewed study published April 14 in BMJ Open.

Researchers from UCLA, the University of Alberta, and Wake Forest tested five chatbots—Gemini, DeepSeek, Meta AI, ChatGPT, and Grok—on 250 health questions covering cancer, vaccines, stem cells, nutrition, and athletic performance. The results: 49.6% of responses were problematic. Thirty percent were "somewhat problematic," and 19.6% were "highly problematic"—the kind of answer that could plausibly lead someone toward ineffective or dangerous treatment.

To stress-test the models, the team used an adversarial approach—deliberately phrasing questions to push chatbots toward bad advice. Questions included whether 5G causes cancer, which alternative therapies are better than chemotherapy, and how much raw milk to drink for health benefits.

"By default, chatbots do not access real-time data but instead generate outputs by inferring statistical patterns from their training data and predicting likely word sequences," the authors write. "They do not reason or weigh evidence, nor are they able to make ethical or value-based judgments."

That's the core problem. The chatbots aren't consulting a doctor—they're pattern-matching text. And pattern-matching on the internet, where misinformation spreads faster than corrections, produces exactly this kind of output.

The researchers continue: "This behavioural limitation means that chatbots can reproduce authoritative-sounding but potentially flawed responses." Out of 250 questions, only two prompted a refusal to answer—both from Meta AI, on anabolic steroids and alternative cancer treatments. Every other chatbot kept talking.

Performance varied by topic. Vaccines and cancer fared best—partly because high-quality research on those subjects is well-structured and widely reproduced online. Nutrition had the worst statistical performance of any category in the study, with athletic performance close behind. If you've been asking AI whether the carnivore diet is healthy, the answer you got was probably not grounded in scientific consensus.