Vitamin B12 is absorbed into the body rapidly. Consequently, while you may start to feel benefits within 48-72 hours, moreover it can take up to 3 months to experience the full effects due to the red blood cell reproduction cycle. Moreover, some individuals may require more than one injection to achieve the maximum impact. We recommend that clients schedule a booster every 12 weeks. However, individual needs vary, and you will be able to gauge when your body requires a boost.