Any excessive amount not used by the body is flushed out in the urine due to vitamin B12 being a water soluble vitamin
As you titrate on the same concentration: 4 mg = 0.80 mL = 80 units, 8 mg = 1.60 mL = 160 units (this exceeds a single 100-unit barrel, so it is drawn as two fills), and 12 mg = 2.40 mL = 240 units (drawn across multiple fills)
Common injection sites include the abdomen (avoiding the area immediately around the navel), anterior thigh, or upper arm
Long-term use of metformin or proton pump inhibitors (PPIs) impairs B12 absorption over time
Finer than 27 gauge should not be used, because of the danger of it breaking whilst in your flesh
Measure carefully with a 3 mL syringe, not an insulin syringe which maxes out at 1 mL and would require multiple draws