Four weeks might work for a fresh injury, but it is often too short for chronic, long-term conditions
Pogribna M, Melnyk S, Pogribny I, Chango A, Yi P, James SJ: Homocysteine metabolism in children with Down syndrome: in vitro modulation
J Pediatr (1997) 130(1):13845.10.1016/S0022-3476(97)70323-8 48 BugianiMLamanteaEInvernizziFMoroniIBizziAZevianiMet alEffects of riboflavin in children with complex II deficiency

Major Ingredients Water, Glycerin, Dipropylene Glycol, Propanediol, Hippophae Rhamnoides Water, Caprylic/Capric Triglyceride, PPG-13-Decyltetradeceth-24, Hydroxyacetophenone, Caprylyl Glycol, Carbomer, Tromethamine, Hydrogenated Lecithin, Glutathione(600 ppm), Cetearyl Alcohol, 1,2-Hexanediol, Disodium EDTA, Stearic Acid, Dipotassium Glycyrrhizate, Terminalia Ferdinandiana Fruit Extract, Butylene Glycol, Lecithin, Pentylene Glycol, Acetyl Glutamine, Sodium Hyaluronate, Polyglyceryl-10 Stearate, Panthenol, Folic Acid, Bacillus/Soybean Ferment Extract, Oligopeptide-1, Hexapeptide-11, Oligopeptide-2, Oligopeptide-3, Sodium Ascorbyl Phosphate, Hydrolyzed Pea Protein, Madecassoside, Phytosterols, Squalane, Olea Europaea (Olive) Fruit Oil, Tocopherol, Niacinamide, Hyaluronic Acid, Hydrolyzed Hyaluronic Acid, Hydroxypropyltrimonium Hyaluronate, Hydrolyzed Sodium Hyaluronate, Potassium Hyaluronate, Ceramide NP, Butyrospermum Parkii (Shea) Butter, Ethylhexylglycerin, Biotin, Sodium Hyaluronate Crosspolymer, Pyridoxine, Cyanocobalamin, Riboflavin, Thiamine HCl, Retinol, Bioflavonoids, Sodium Acetylated Hyaluronate, Menadione, Acetyl Hexapeptide-8, Copper Tripeptide-1, Palmitoyl Pentapeptide-4, Linoleic Acid, Beta-Carotene, Fragrance Ingredients subject to change at manufacturer's discretion

did during his appearance on Rogans podcast
Vitamin B12 has a very low risk of toxicity, so there's really no upper limit to how much you can take without harm