Insulin is classified based on how quickly it takes effect. There are fourcategories:
Rapid acting should be taken just before or just after eating. It begins to lower blood glucose in less than 15 minutes.
Short acting should be taken 30 minutes before a meal. It begins to lower blood glucose within 30 minutes to 1 hour.
Intermediate acting has an effect for 14-20 hours, depending on the type, so it is typically only taken once per day.
Long acting has an effect for 20-30 hours, depending on the type, so it is only taken once per day.
Insulin can be packaged in vials, pens/cartridges, or inhaled.