Jama 327 (12), 1194
In case of discomfort or unfavorable symptoms, discontinue immediately and contact your physician
Vitamin B12 is naturally found in animal products, including fish, meat, poultry, eggs, and dairy
Disclaimer: In China it is available as an OTC supplement
Add to this the complexity of modulation of topicals (skin irritation, skin threshold, cycling etc..The whole melasma treatment process can get very complex indeed, & that is before we even add any lasers or novel peels (of which there are over 20 methods in 5 to 10 settings or combinations)
Biochem J 262:881885 Bailey CJ, Mynett KJ, Page T (1994) Importance of the intestine as a site of metformin-stimulated glucose utilization