From Remedy to Risk: A Contemporary Case Report of Methemoglobinemia Caused by Unregulated Intake of a Herbal Product.

Methemoglobinemia is a rare but potentially fatal disorder characterized by tissue hypoxia secondary to oxidation of haemoglobin's ferrous iron (Fe²⁺) to ferric iron (Fe³⁺), which diminishes the blood's oxygen-carrying capacity. We report what is, to our knowledge, the first case from India of acquired methemoglobinemia following ingestion of an unregulated online herbal remedy for arthritis, highlighting a rare and under-recognized cause. A 52-year-old male patient developed acute central cyanosis and persistent hypoxia after consuming an online product containing olive oil and salt. Despite high-flow oxygen, saturation levels remained low, and co-oximetry revealed methemoglobinemia (40%). Timely intravenous methylene blue led to a rapid and complete recovery. This case underscores the importance of considering methemoglobinemia in the differential diagnosis of unexplained hypoxia, especially among patients with a history of alternative or unregulated product use, and highlights the need for increased vigilance regarding online supplements in clinical practice.