Benefits of B12 injections include the following: Might Reduce Depression, Cognitive Decline and Dementia: Some studies show that, especially in older people, supplementing with vitamin B12 can help prevent depression, restore better mood control and retain healthy memory/mental functioning
The technique is learnable, but the decisions around it (do you actually need it, what dose, how often, and is something else being missed) are medical judgements, and getting them wrong carries real cost
If you already have a diagnosed deficiency under NHS care and your symptoms return before your next scheduled dose, that is a conversation to have with your GP, who can review the schedule
Gently aspirate by pulling back slightly on the plunger to check for blood: If blood appears , stop, withdraw, and restart in a new spot