vitamin b12 and vitamin c injection at a Licensed Pharmacy B12 Shots vs. IV Infusions:

(23) How Long Does It Take Vitamin B12 To Work

A tolerable upper intake level (UL)the amount you can safely take without risk of severe side effectswas never set for it because it has a low potential for toxicity, and the body does not store it in excess (NIH-a, 2021)

Intramuscular injections deliver a concentrated dose directly into the blood flow and provide the highest bioavailability of active ingredients and an immediate start of action

This is not a health side effect per se, but it is a consequence of use that certain populations must consider

DNA was not isolated from the first two samples collected in the LD/LD-V group, and the first sample collected in each of the other respective groups, due to the use of saline to flush the cecum (after weighing) during early collection (therefore, n = 25 cecal samples)