They are selected for their location, cleanliness, and quality
A test helps confirm whether B12 is actually the issue and whether there may be other causes of fatigue
The most common form of vitamin B12 in dietary supplements is cyanocobalamin, but other forms include adenosylcobalamin, methylcobalamin, and hydroxycobalamin
One important consideration: a 5mg vial reconstituted with 2mL of water gives you excellent measurement precision at the 1mg dose level (40 units, very easy to read), but the 4mg dose would require 160 units, far exceeding the syringe
Or better yet, consider the reconstitution math before purchasing
Is a B12 injection better than oral supplements