In research discussions, exposure durations vary widely depending on study design
However, if you do not have good skin elasticity, this is not the best procedure for you
[2] in 2016 was the main interventional study on which the ADA has relied since 2017 to recommend regular monitoring of vitamin B12 levels in individuals treated with metformin, particularly in the presence of neuropathy or anemia [9]
If a B12 deficiency is the only thing causing your palpitations, you could start feeling better within a few weeks to a couple of months
A doctor can confirm the diagnosis, figure out the right dose and form of B12 for you, and make sure nothing else is being missed.
Think of weekly shots as focused, short-term work to fix a specific problem, and monthly shots as ongoing upkeep once you are stable