reaction to b12 injections Common & Rare Side Effects of Vitamin Vitamin B12 Injections: Benefits and
Description
Luke's Hospital lists the following drugs as those that might possibly interact with B12 injections

Regular check-ups are important to make sure your B12 therapy is working right

It should be kept in mind that although B12 injections are quite effective, they are not fairy dust
The injection appointments themselves take under 15 minutes, so feel free to stop by during your lunch break

doi: 10.1073/pnas.90.24.12035