is there a b12 injection Compounded Cyanocobalamin (Vitamin B12) Vitamin B12 Injection: Energy Boost
Description
When they do not function properly, overall cellular health declines

Vitamin B12 & Pregnancy: A Nutrient Crucial for Your Babys Health Vitamin B12 also known as cobalamin is used in the creation of new DNA, proteins, and lipids

[2] So deficiency is more common than people think
Oral Cobalamin Supplementation in Cats with Hypocobalaminaemia: A Retrospective Study

Results are most effective when paired with proper nutrition and regular movement