Side effects that you should report to your primary care physician as soon as possible: Allergic reactionsskin rash, itching, hives, swelling of the face, lips, tongue, or throat Change in vision Dehydrationincreased thirst, dry mouth, feeling faint or lightheaded, headache, dark yellow or brown urine Gallbladder problemssevere stomach pain, nausea, vomiting, fever Heart palpitationsrapid, pounding, or irregular heartbeat Kidney injurydecrease in the amount of urine, swelling of the ankles, hands, or feet Pancreatitissevere stomach pain that spreads to your back or gets worse after eating or when touched, fever, nausea, vomiting Thoughts of suicide or self-harm, worsening mood, feelings of depression Concerns for thyroid cancer new mass or lump in the neck, pain or trouble swallowing, trouble breathing, hoarseness Concerns for pancreatitissevere stomach pain that spreads to your back or gets worse after eating or when touched, fever, nausea, vomiting This list may not describe all possible side effects

Which is not to say he supports the change
Journal of Endocrinology (2002) 4
Do B12 Injections Give You More Energy If You Are Not Deficient
While patients may encounter bold claims online regarding accelerated recovery, anti-aging effects or enhanced performance, those claims have not been established through robust clinical research