"A pilot study comparing the pharmacokinetics of injectable cyanocobalamin and hydroxocobalamin associated with a trace mineral injection in cattle"
The vitamins may take some time to fully absorb into the body, meaning with injections it may take a few days or weeks before the effects are noticeable, and may take a bit longer for vitamin supplements, but at the recommendation of a doctor, you should feel better with the correct amount of vitamin B12 being taken regularly
[PubMed | ClinicalTrials.gov | DOI] Rubino D, Abrahamsson N, Davies M, et al
however, injections may be administered biweekly until vitamin B12 levels return to normalcy
Freezing is even worse because ice crystals physically damage the peptide structure, causing irreversible denaturation