Question of the Day:, How long does it take for a B12 injection to rev up the engines of energy? , For many people, the boost can be felt within 2448 hours. Others may notice gradual changes What Are B12 Injections? And Are They Safe? OmegaQuant Injection is a technique for delivering drugs by parenteral administration, that is, administration via a route other than through the digestive tract. Parenteral injection includes subcutaneous, intramuscular, intravenous, intraperitoneal Mecobalyn PFS zucipharma Ivy Grove Surgery : Self administration of B12 injection