It’s common knowledge that you should never use needles more than once. For those of you that are unsure why here’s a brief overview. First of all the tip of a needle is sharp and fine, so that it goes into the skin easily when you inject. Every time you use a needle, it gets blunter and loses sharpness. The more times you use it, the blunter it gets. This makes it harder for the needle to pierce the skin, and thus more painful when you do the injection. This is not only done to avoid painful injections, but to ensure that you avoid infection by using a fresh, clean needle. This also reduces bleeding and bruising. The tip of a needle can also weaken and break off and get stuck under your skin. Most needles are designed to only be used once.
Also needles spread all sorts of diseases like Hepatitis A, Hepatitis B and so many other fatal diseases, so usage of the same needle for saving money is really not worth it.