Understanding the B12 Vitamin Shot: Benefits, Risks, and Dosage Guide For some, the day doesn't begin until the first cup of coffee. But for others, that ritualfamous for bringing focus and energycan cause a racing heart, jittery hands, and a vague sense 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, Vitamin B12 Injection Side Effects and Safety Feeling Tired All the Time? It Might Be a Vitamin B12 Deficiency Fusion HealthCare