Human evidence for precursors is mixed: some trials report good safety, but metabolic endpoints such as insulin sensitivity have not consistently replicated in people
Long-term human safety data does not exist
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However, once diagnosed it presents a difficult management problem in patients suffering from pernicious anemia, as there is no substitute
There are some very rare side effects listed in medical literature (mostly when large doses are given): for example, one out of many thousands of patients might develop a disturbance in liver enzymes or a tingling in the fingers or toes
While that initial boost is great, the real goal is to maintain your B12 levels over time so you can enjoy sustained energy and focus without the ups and downs