This is because they dont need to be digested, which avoids the risk of low absorption
B12 is notoriously hard to absorb through the gut, especially as you get older or if you have certain digestive issues
For NNMT assays remember that the compound competes at the nicotinamide substrate site, so the apparent potency depends on the nicotinamide concentration used
If you experience severe pain, signs of infection (redness, warmth, swelling), or an allergic reaction (rash, itching, difficulty breathing), seek medical attention immediately
It can take a few weeks to a month to notice the effects of B12 shots, since your body has to replenish your stores of this vitamin