What doesn't mix with what in a syringe?

[PatBateman]

You can put whatever gear, or in your case B12, into your syringe. I like the lava lamp look of B12 with test. Be careful injecting it though because if your oil is going in and you have a certain amount of pressure on the plunger pushing it in and then the B12 hits the pin and you don't let up your going to shoot that B12 really hard and it will hurt. So keep an eye on it.

this is a very good point, the two different bases have completely different viscosities.