B12 Side Effects: Too Much of a Good Thing? Side Effects of Vitamin B12 Injection Essential Guide 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, Wow guys, you've been gate keeping!! Got my first B12 injection last week and it's like I am awake for the first time since having kids 20 years ago It's