b12 injections im How to Give at Home to Yourself · PA Relief The Truth About B12 Injections:

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People who are on certain dietary restrictions, especially vegans and those undergoing a weight loss regimen, may have a higher chance of developing vitamin B12 deficiency

This includes the Vitamin B12 injections dosage and how often to get them

People who've had gastric or bariatric surgery, or who have an ileostomy, are commonly unable to absorb enough vitamin B12 from their diet or a supplement so are likely to need injections via their GP

Summary Vitamin B12 deficiency isnt likely to be a cause for hair loss

First, verify your source and purity