There's more dramatic license than just that - if you inject yourself into your behind, there's no way a "pressurised stream of blood spurted halfway across the room". Not going to happen.

I have the "fortune" of having to do injections in that place every week for several years running now, and I'm far from handy with a needle. The worst that ever happened was a thin rivulet. And that was dramatic - usual is nothing, or maybe a drop or two of blood.

Based on that part alone, he's dramatically exaggerating. Combine that with having every side effect in the book, and my money is on this being made up in large parts.