Vitamin B12 deficiency symptoms: Metallic taste in your mouth can mean you're lacking B12 Express.co.uk 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, Feeling worse after B12 Injection: Answering concerns. La Vie Med Spa Feeling worse after B12 Injection: Answering concerns. La Vie Med Spa Oral manifestations in vitamin B12 deficiency patients with or without history of gastrectomy BMC Oral Health Springer Nature Link