why do i feel tired after a b12 injection Feeling tired, foggy, or running on empty lately? Vitamin plays big role in energy, brain function, and red blood cell health., When levels are low, you might notice fatigue, poor focus, or low Vitamin B12 Side Effects

But youve gotta give it time to build up enough B12 reserves first

These may include mild digestive changes (nausea, altered bowel movements), increased energy levels that may feel stimulating initially, mild headaches (often related to dehydration), and minor injection site reactions (redness, temporary discomfort)

Insert the needle at a 4590 angle, depending on needle length and body type

Wellness 20 July 2025 7 min read Needle Size for a B12 Injection: A Simple Guide By Alaiyka Parvez Owner, CoLaz Aesthetics Clinic The short version For an intramuscular B12 injection, the usual choice is a 22 to 25 gauge needle, 1 to 1.5 inches long, given at 90 degrees into the deltoid