The appeal is so strong that people are injecting the stuff daily or a few times a week
Why does L-Carnitine contain MAH

Immediate medical attention (emergency department or urgent care) is warranted for: Signs of anaphylaxis or severe allergic reaction, including difficulty breathing, throat tightness, rapid pulse, dizziness, or widespread urticaria (call 911) Severe swelling extending beyond the injection site or involving the face, lips, or tongue Signs of significant infection, including fever above 100.4F (38C), purulent drainage, or rapidly spreading erythema with warmth Severe pain disproportionate to visible findings Skin necrosis, blistering, or ulceration at the injection site Scheduled healthcare provider evaluation is appropriate for: Persistent injection site reactions lasting more than 5 to 7 days despite conservative management Recurrent moderate to severe reactions with each injection, suggesting possible hypersensitivity Development of indurated nodules or lipohypertrophy at injection sites Uncertainty about whether symptoms represent normal reactions or require intervention Clinical assessment of concerning injection site reactions typically includes examination of the affected area, review of injection technique, and evaluation for signs of infection or hypersensitivity

Noh Y et al
it is not a substitute for professional medical consultation, diagnosis, or treatment
The injection delivers B12 directly into the bloodstream, making it the most reliable method for patients with absorption problems, pernicious anaemia, or gastrointestinal conditions affecting B12 uptake (such as Crohn's disease, coeliac disease, or following gastric surgery)