We explain, in plain language with no jargon, the main types of insulin and how they differ.
This guide is educational and general: it isn't meant for adjusting doses or replacing the regimen your doctor or diabetes educator has prescribed. The type, dose and timing of insulin should always be decided with your medical team, on an individual basis.
The basic idea: "basal" insulin and "bolus" insulin
A normally functioning pancreas releases insulin in two ways: a little continuously throughout the day (to keep glucose stable between meals and overnight) and a lot more all at once when eating (to handle the glucose rise from that meal). Insulin treatments try to mimic that same pattern by combining two types of insulin with different profiles: a slow-acting insulin that acts as "basal insulin" (the background level) and a fast-acting insulin that acts as "bolus insulin" (the one that covers meals). The rest of the insulin types are, essentially, variations on these two profiles.
Quick comparison of insulin types
These times are approximate: they can vary from person to person and depending on where on the body the injection is given. Data based on the CDC's types of insulin (U.S. Centers for Disease Control and Prevention).
Each type of insulin, explained in more detail
Ultra-rapid (rapid) insulin
This is the fastest-acting insulin. Since it starts working almost immediately, it's used to cover what's eaten at each main meal, which is why it's normally injected right before (or, in some cases, right after) starting to eat. When is it used? Injected right before eating, to cover the glucose rise from that meal.
Short (regular) insulin
One of the oldest insulins, it takes somewhat longer to start working than ultra-rapid analogs, so it needs to be injected further ahead of the meal. Today it's used less often than the more modern rapid-acting insulins. When is it used? Injected 30 to 60 minutes before eating.
Intermediate insulin
It acts more slowly and for longer, covering insulin needs for much of the day or night. It's commonly combined with a rapid-acting insulin to also cover what's eaten at meals. When is it used? Covers half the day or the night; usually combined with a rapid-acting insulin.
Long-acting (basal) insulin
Known as "basal" insulin: it isn't meant to cover a specific meal, but to maintain a stable background insulin level throughout the day, similar to how a normally functioning pancreas would behave between meals. When is it used? Provides a stable background level for nearly the whole day, without direct relation to meals.
Ultra-long-acting insulin
Works similarly to long-acting insulin, but lasts even longer and its effect is even more stable, which in practice can give a bit more leeway if an injection is delayed one day from the usual schedule (always as directed by the medical team). When is it used? Very long-acting basal insulin, with more flexibility in timing.
Premixed (biphasic) insulin
Combines a portion of short- or rapid-acting insulin with an intermediate-acting portion in a single injection, at a fixed ratio. It simplifies the number of daily injections, though it offers less flexibility to adjust each component separately. When is it used? Injected 10 to 30 minutes before breakfast and dinner.
Common questions
Why are there so many different types of insulin?
Because each person needs a different combination of "background" insulin and "mealtime" insulin, depending on their routine, schedule and type of diabetes. Having several types with different speeds and durations makes it possible to tailor treatment to each case.
What's the difference between human insulin and insulin analogs?
Human insulin (like regular or NPH) has a structure identical to the one the human body produces. Analogs (like lispro, aspart, glargine or degludec) are insulins slightly modified in the lab so they act faster or for longer, depending on the case. Both types are real insulins that have been used safely under medical prescription for decades.
Can different types of insulin be mixed in the same syringe or pen?
It depends on the specific type of insulin: some combinations are designed to be mixed (like premixed insulins) while others shouldn't be mixed together. This should always be indicated by the medical team, since mixing insulins incorrectly can change how they work.
Is all insulin given the same way?
The most common way is subcutaneous injection (with a pen, syringe or insulin pump), though the device and injection site can slightly affect how quickly it acts. You can see how insulin pumps work, using rapid-acting insulin continuously, in our insulin pump comparison.