There are quite a few different types of insulin on the market and a whole bunch of brand new ones arriving soon.
The basic broad classification is long vs short acting. As their name implies they are long or short acting. What does that mean? When you require insulin you have both basal needs as well as prandial (meal time) needs. Your basic and ongoing metabolism needs glucose to go into the cells (all the cells in the whole body) on a minute to minute basis and hence a basal requirement of both glucose and insulin. Insulin is the key that gets the glucose in. When you eat carbohydrates you then require insulin to get the glucose load out of the blood circulation and into the cells where it can be used as fuel.
The long acting insulins cover basal requirements and act for a long time – 6 – 24 hours and some new long actings with a duration of about 48 hours.
The short acting insulins act for a short period of time, starting within about half an hour of injecting and then lasting for around 4 hours. There are brand new ultra short acting ones that are soon to arrive.
Insulin is a dangerous substance and the most acute danger is hypoglycaemia. In other words you inject too much insulin and the sugar plummets very low. At different levels for different people but generally below 2.5 mol/l you not only feel awful but can become unconscious and potentially no longer require a bucket list.
For this reason it is imperative that if you are injecting insulin you understand how it works, when it starts working, how long it works for, the shape of the curve of the action and also imperative to know what your number is – your blood glucose. Before injecting insulin you should ideally do a glucose test and factor this number into the equation.