Is it possible to replace normal tablet medication with a (needle) shot instead?

Consult with your doctor regarding any switch from pills to shots. Some drugs can be delivered both ways but the dose may have to be adjusted (some drug may be lost due to digestion). Also ask your doctor about probiotics to help bowels.

There are a lot of things involved, and it would be an exceptionally bad idea to inject anything, especially directly into your veins, without knowing the exact effect and amount to use.

Years ago out of necessity I had a roommate who used to make syringes of a migraine medication, because he knew the factory syringes held 6 mg of the drug compared to 50 mg in the tablets, so he could turn one dose of the very costly drug into seven or eight. He also knew the drug was water-soluble and that the binding agent (what holds the tablet together) was not, and he had access to sterile syringes, needles, sterile saline, and sterile mixing vials and was familiar with aseptic technique. This was for subcutaneous injections (under the skin) and not for intravenous injections (into the vein).

Definitely NOT RECOMMENDED.

Although i dont suggest doing this, its just a idea you can consider and choose to do yourself, you could dissolve a tablet into a saline solution and inject it.