It is the most common route for musculoskeletal applications because it allows proximal injection near the injury site, which appears to improve local tissue concentration based on animal study findings
They measured the full B12 body count of four people and found it to be 780 to 1,350 g of B12 with a daily loss of 0.12% for a maximum loss of 1.6 g per day or 11.2 g per week
(PubMed) Wang H, Li L, Qin LL, Song Y, Vidal-Alaball J, Liu TH
A handful of other masking agents are also banned including probenecid, desmopressin, and vaptans to prevent the concealment of other banned agents in doping control samples
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Several types of meat contain plenty of niacin, including chicken