High-dose methylcobalamin in amyotrophic lateral sclerosis: mechanistic rationale, translational evidence, and clinical implications

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurodegenerative disorder characterized by selective degeneration of upper and lower motor neurons, driven by converging mechanisms including glutamatergic excitotoxicity, mitochondrial dysfunction, oxidative stress, calcium dyshomeostasis, impaired RNA metabolism, and neuroinflammation. In the absence of effective disease-modifying therapies, high-dose methylcobalamin has emerged as a candidate intervention based on its pleiotropic neurobiological effects. A structured literature search was conducted in PubMed/MEDLINE and ScienceDirect to identify peer-reviewed studies published between January 2017 and December 2025 addressing the mechanistic, preclinical, and clinical effects of methylcobalamin in ALS. Preclinical evidence suggests that methylcobalamin modulates homocysteine metabolism, supports S-adenosylmethionine-dependent methylation pathways, preserves mitochondrial integrity, attenuates oxidative stress, and promotes axonal regeneration. Experimental and translational findings further indicate that its therapeutic effects may be strongly dose dependent, particularly under ultra-high-dose regimens capable of overcoming limitations in central nervous system delivery. Clinical trials evaluating ultra-high-dose methylcobalamin demonstrate a potential attenuation of functional decline in patients treated during early disease stages, although effects on survival and respiratory outcomes remain inconsistent. This narrative review integrates molecular mechanisms, experimental evidence, biomarker research, and clinical trial data to examine the translational relevance, stage dependency, and therapeutic implications of high-dose methylcobalamin in ALS.