Taking Vitamin B12? Read this first. While B12 is often hailed as a safe energy and brain booster, many real users are reporting unexpected side effects including anxiety, insomnia, When I first got the B12 shot, I was really surprised what a difference it made in my energy levels. And thats exactly what happens if youre deficient in this essential vitamin. , B12 is involved in B12 Shots for Energy: Do They Work, Who Needs Them & What to Expect Greenwich Medical Spa Feeling worse after starting B12 : r B12_Deficiency