vitamin b12 injections good or bad healthline 9 Best Supplements Are Vitamin B12 Shots Right
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[1] Unlike fat-soluble vitamins that accumulate in body tissues, water-soluble vitamins are generally excreted through urine when consumed in excess

If you have a compromised digestive system you may need extra B12

This case demonstrates that early intervention with B12 supplementation can cause reversal of both central and peripheral nervous system dysfunction

Think of it like layering skincare, but for your insides
Often within a few days, especially if you were running low to begin with