How do Vitamin B12 Injections work?

How do Vitamin B12 Injections work?
According to the UK government, our bodies require 1.5 micrograms (mcg) a day of Vitamin B12, although other governments advise that we actually need more.
Vitamin B12 is predominately only acquired naturally from animal-based produce such as meat, dairy, eggs, as well as fish, especially trout, salmon and cod. Vitamin B12 deficiencies are therefore quite common among vegetarians and vegans. However, many people who are deficient are simply this way because their bodies are unable to absorb Vitamin B12 efficiently.
Supplementary tablets can be taken to account for a lack of Vitamin B12 in the diet. However, injections are a more effective method because the Vitamin B12 is delivered straight into your system without being digested first, allowing for maximum results. Any Vitamin B12 that is not required by the body is excreted in the urine.