Vitamin B-12 shots are taken to boost energy and are recommended for individuals who are unable to absorb dietary B-12 through specific foods, according to SFGate. B-12 is a nutrient that aids the heart and brain and also supplements the creation of red blood cells.
Besides being taken as a shot, B-12 can also be taken under the tongue where it is sent directly into the bloodstream, notes SFGate. B-12 shots are used to treat depression, fatigue, restless legs syndrome, autism and Bell's palsy. Elderly individuals with poor mental faculties might also be prescribed a B-12 shot.
When taken as a shot, B-12 is administered through the muscle of the thigh or the upper arm, according to SFGate. A person who has a B-12 deficiency typically receives 1,000 micrograms of B-12 for 10 days before switching to one shot a week for four weeks. The person receives a single shot once a month for the duration of his life. When taken to improve mental faculties, the person receives 1,000 micrograms every day for five days before switching to one shot per month for five months.
Common causes for vitamin B-12 deficiency include poor absorption or inadequate dietary sources if individuals choose not to consume meat, seafood or dairy, which are three common sources of B-12, notes SFGate.