S-methylmethionine (SMM, also known as vitamin U) is a sulfur-containing vitamin-like compound that has been investigated since the 1940s for its gastroprotective and cytoprotective properties. Historically derived from observations of antiulcer activity in plant-derived foods, SMM has been studied in preclinical models and limited clinical settings for its multilevel pharmacological effects. This narrative review critically evaluates the available evidence on SMM’s pharmacological actions across organ systems, with explicit differentiation between preclinical and clinical data. It covers the most consistently reported gastroprotective and antiulcer effects, as well as antioxidant, anti-inflammatory, cytoprotective, and regenerative activities observed predominantly in preclinical studies. Particular attention is paid to organ-specific protection in the nervous system, liver, kidneys, lungs, skin, eyes, and oral tissues, although human evidence remains scarce. Proposed mechanisms are mediated primarily through suppression of oxidative stress, modulation of inflammatory and immune responses, maintenance of glutathione homeostasis, activation of ERK/NF-κB and Nrf2/Keap1 pathways, and regulation of methylation processes. Building on recent descriptive reviews, this work provides a structured critical synthesis that grades evidence quality, compares SMM with the structurally related methyl donor S-adenosylmethionine (SAMe), and analyses the translational and regulatory barriers that have prevented Western drug registration despite over 70 years of investigation. Despite a substantial preclinical evidence base and historical clinical observations, the level of evidence for many indications remains limited. Well-designed Phase II randomized controlled trials and innovative pharmaceutical formulations (especially topical and mucosal delivery systems) are urgently needed to translate preclinical promise into clinical benefits.

Acute otitis media is an inflammatory disease affecting all compartments of the middle ear, characterized by localized pain, fever, hearing impairment, and, occasionally, purulent exudate. It represents a significant clinical concern in both pediatric and adult populations, with approximately 709 million cases reported annually worldwide, 51% of which occur in children. However, currently available topical otic formulations are limited by their inability to achieve predictable therapeutic concentrations at the site of inflammation, resulting in reduced efficacy. In addition, the selection of appropriate active pharmaceutical ingredients (APIs) for drug products remains challenging; as a result, existing therapies do not comprehensively address all stages of pathogenesis. This study aimed to analyze existing locally acting formulations for middle ear drug delivery, evaluate their advantages and limitations, and assess modern approaches to the development of novel drug delivery systems and API combinations. A critical review of 69 publications (2010–2026) was conducted, supplemented by a strengths and limitations analysis of dosage forms and an evaluation of APIs based on clinical data. The findings highlight a lack of targeted drug delivery systems, limited efficacy of existing API combinations against bacterial biofilms, and their risk of ototoxicity. Emerging innovative drug delivery approaches, including microemulsions, vesicular systems, stimuli-responsive systems, and hydrogels, have demonstrated promising results in preclinical studies; however, their efficacy and safety remain to be confirmed in clinical settings before their full therapeutic potential in otitis media treatment can be realized.