Both pills and injections have excellent safety profiles
Ultimately, the choice is up to you (and your doc)
Addisonian anemia Gastrointestinal pathology, dysfunction, or surgery Fish tapeworm infestation Folic acid deficiency Malignancy of pancreas or bowel Vitamin B12 Injection Side Effects There is no reported server side effects of vitamin B12 injections
Severe loss of quality of life, due to symptoms such as debilitating fatigue, insomnia (B12 is required for synthesis of melatonin), mental illness, and neurological symptoms
For the push, I routinely stick (pun intended) to a 23 gauge needle, though your doctor or pharmacist may have their own opinions on needle gauge or even syringe volume
B12 supports normal energy metabolism and red blood cell production, so correcting a genuine deficiency can help you feel and perform like yourself again, but shots are not a proven performance enhancer for people who are not deficient