Digestive problems, like constipation and diarrhea, can be caused by not getting enough B12
Mood Balance: Supports emotional stability and positive outlook
[24] Cyanocobalamin is one of the most widely manufactured vitamers in the vitamin B 12 family (the family of chemicals that function as B 12 when put into the body), because cyanocobalamin is the most air-stable of the B 12 forms, [25] and is the easiest to purify after it is produced by bacterial fermentation
The 2-4 week window is not a hard cutoff
Additional benefits to boosting your B12 include improved memory and cognition, better eyesight, and a healthier nervous system (via MSN)

Vitamin B12 shot may be prescribed to prevent or treat the following: Pernicious anemia (a condition in which there are low red blood cell counts due to an abnormality in B12 absorption by the intestines) Megaloblastic anemia (a type of anemia in which there are very large red blood cells called megaloblasts) Cognitive disorders, such as dementia (a disorder characterized by problems with memory, problem-solving abilities, language, etc.) Disorders that affect B12 absorption, such as pancreatic diseases, intestinal infections, Crohns disease, and tropical sprue Cardiovascular disease risk (by lowering blood homocysteine levels, which is a compound associated with an increased risk of heart problems) Multiple sclerosis symptoms Bells palsy recovery B12 deficiencies related to: Weight loss Vegan or restrictive diets Surgery to remove the part of the stomach or the ileum (the last part of the small intestine) Energy and endurance What are signs of vitamin B12 deficiency