b12 injection skin rash from Understanding the B12 Vitamin Shot: Benefits, Risks, and Dosage Guide P484 Cobalt as the culprit:
Description
Consider the following: In Japan, ultra-high daily doses of methyl B12 (25,000-50,000g per shot) have been used to extend the survival of ALS patients
Adipocyte differentiation and fat-metabolism models

Here are some common scenarios: Initial Treatment Phase: In the initial phase of treatment, injections may be administered more frequently, such as daily or weekly, until B12 levels are restored

What Is Vitamin B12 and Why Is It So Important

Feeling tired and worn out

Thiamine-responsive megaloblastic anaemia syndrome (TRMA) resembles B12 deficiency
