It's been three years for me. I switched from abdomen area to butt cheek fairly quickly. Once in awhile a get some blood. As long as the bubbles in the dose aren't huge you're fine. Quality of the needle is key and can affect amount of pain, ease of injection and how well the T plunges through. When I first started I used the needles that came with my refills. Then I started buying them wholesale online in bulk. A box of 200 for $10 or something. They last forever but they are not as good as the old reifll needles. The angle of the tip, the coating, the quality of the metal used, all of that can make it more difficult to inject. My current batch ain't great but I'm using them all! I've gotten to a point where it can be hard to find a spot that hasn't been pricked and that hurts.