Imean rapid insulin n long effect one, Apidra, aspart,n the grey colour pen insulins? ## Well, you've already specified the differences. There are some that work fast to bring your blood sugar down, which means they also don't work that long in the body, so they usually require more frequent dosing or must be followed by one of the other ones. The long acting are exactly that, they last longer in the body to help control your blood sugar for a longer period of time. The problem with them, however, is that they can take a bit to start working, so someone's sugar may rise for awhile, before it starts to bring them down. That's why they're often combined with a short acting. Learn more Insulin details here. Are you diabetic and using insulin?