The NIH's LiverTox database — a comprehensive, peer-reviewed reference maintained by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) — updated its entry on Ilex paraguariensis (yerba mate) in November 2024. The update assigned yerba mate a likelihood score of 'D' on the LiverTox hepatotoxicity scale, meaning it is classified as a 'possible but rare cause of clinically apparent liver injury.' While this is the second-lowest risk rating on the scale (below A, B, and C), it reflects the first formal acknowledgment by a major reference database that yerba mate can cause documented liver damage.
The Index Case
The case that precipitated the updated classification involved a 21-year-old American man who presented with jaundice and pruritus (itching) after consuming yerba mate daily for approximately four months. Laboratory evaluation revealed a 'strikingly hepatocellular' injury pattern — meaning the damage was concentrated in liver cells (hepatocytes) rather than the bile ducts — with significantly elevated liver enzymes. The patient had no history of pre-existing liver disease, alcohol abuse, or concurrent medication use that would explain the injury. After discontinuation of yerba mate, his liver function tests normalized within approximately two months.
The Proposed Mechanism
The LiverTox entry notes that the chemical compound responsible for liver injury from yerba mate has not been identified, but the clinical features of the reported case are consistent with an immunologically mediated mechanism — an idiosyncratic hypersensitivity reaction in which the immune system attacks liver cells in response to a metabolite of the ingested compound. This pattern is similar to rare hepatotoxicity cases associated with green tea extract and turmeric (curcumin), both of which contain polyphenols that are metabolized in the liver and can, in genetically susceptible individuals, trigger immune-mediated injury.
Context: Population-Level Risk
The LiverTox assessment is careful to note that small clinical studies on yerba mate have 'generally reported minimal or no adverse effects, including no mention of hepatotoxicity.' The 'D' classification — possible but rare — reflects a situation in which the population-level risk is extremely low but individual cases have been documented with sufficient clinical detail to establish biological plausibility. In Uruguay, where 85% of adults drink mate daily and per-capita consumption reaches 10 kilograms per year, liver disease attributable to yerba mate has not emerged as a measurable public-health signal.
For the yerba mate industry and for consumers, the LiverTox update is a reminder that no food or beverage is universally safe for every individual. The documented cases are rare enough that they do not warrant population-level health warnings, but they argue for awareness among clinicians evaluating unexplained liver enzyme elevations in patients who consume yerba mate. The practical implication is straightforward: if a patient develops jaundice or abnormal liver function tests, dietary supplement and herbal tea consumption — including yerba mate — should be included in the clinical history.