There are six main types of insulin, categorized by how quickly they start working and how long they last: rapid-acting, short-acting, intermediate-acting, long-acting, ultra-long-acting, and premixed combinations. Within those categories, dozens of brand-name products exist, including concentrated formulations, biosimilars, and even an inhaled version. Understanding the differences comes down to three numbers: onset (when it kicks in), peak (when it’s working hardest), and duration (how long it lasts).
The Six Main Types at a Glance
Every insulin on the market falls into one of these categories based on its timing profile:
- Rapid-acting: Starts in about 15 minutes, peaks around 1 hour, lasts 2 to 4 hours.
- Short-acting (regular): Starts in 30 minutes, peaks at 2 to 3 hours, lasts 3 to 6 hours.
- Intermediate-acting: Starts in 2 to 4 hours, peaks at 4 to 12 hours, lasts 12 to 18 hours.
- Long-acting: Starts in about 2 hours, has no real peak, lasts up to 24 hours.
- Ultra-long-acting: Starts in about 6 hours, has no peak, lasts 36 hours or longer.
- Premixed combinations: Blend two types in a single vial or pen so you get both a quick burst and longer background coverage.
The “no peak” quality of long-acting and ultra-long-acting insulins is a big deal in practice. It means they release a steady, low level of insulin rather than surging and fading, which makes blood sugar easier to predict overnight and between meals.
Basal vs. Bolus: Why Multiple Types Exist
Your pancreas naturally releases insulin in two patterns. It puts out a small, constant trickle all day and night to manage the glucose your liver produces between meals. Then it releases a larger burst whenever you eat to handle the incoming carbohydrates. Insulin therapy tries to copy both of those patterns.
Long-acting and ultra-long-acting insulins serve as “basal” insulin, covering that background need. Rapid-acting and short-acting insulins serve as “bolus” or mealtime insulin, handling the spike that follows food. Some people use only one type; others use both in what’s called a basal-bolus regimen. Premixed insulins bundle both roles into a single injection for people who want fewer shots per day.
Rapid-Acting and Ultra-Rapid-Acting Insulin
Rapid-acting insulin is the most commonly used mealtime insulin. Brand names include Humalog (insulin lispro), NovoLog (insulin aspart), and Apidra (insulin glulisine). You inject it right before eating, and it starts lowering blood sugar within 10 to 20 minutes.
A newer subcategory, sometimes called ultra-rapid-acting, pushes that timeline even faster. Lyumjev appears in the bloodstream within 1 minute of injection and begins its measurable effect about 10 to 13 minutes sooner than standard lispro. Fiasp reaches the bloodstream in roughly 2.5 minutes, compared to about 5 minutes for standard aspart. In real-world terms, these ultra-rapid options start working about 5 minutes earlier than their standard rapid counterparts. That might sound small, but for people trying to prevent sharp post-meal blood sugar spikes, those extra minutes of lead time matter.
Short-Acting (Regular) Insulin
Regular insulin, sold as Humulin R and Novolin R, was the standard mealtime insulin before rapid-acting analogs came along. It takes about 30 minutes to start working, which means you need to inject it well before you sit down to eat. Its longer tail of activity (up to 6 hours) also increases the risk of low blood sugar between meals. Most people who have the option now use rapid-acting insulin instead, but regular insulin is still widely available, often at a lower cost.
Intermediate-Acting Insulin
NPH insulin (Humulin N, Novolin N) is the only intermediate-acting insulin currently available. It takes 2 to 4 hours to begin working, peaks somewhere between 4 and 12 hours, and lasts 12 to 18 hours. That wide peak window is its main drawback: it can cause unpredictable dips in blood sugar, especially overnight. NPH is still used, particularly in premixed formulations, but long-acting insulins have largely replaced it as the go-to background insulin for many people.
Long-Acting and Ultra-Long-Acting Insulin
Long-acting insulins provide a steady baseline for up to 24 hours. Lantus (insulin glargine) is the most widely recognized. Levemir (insulin detemir) was another common option, though it was discontinued in the U.S. at the end of 2024. Several biosimilar versions of glargine are now available at lower cost, including Semglee and Rezvoglar, both FDA-designated as interchangeable with Lantus.
Ultra-long-acting insulin goes a step further. Tresiba (insulin degludec) lasts 36 hours or more, which gives you more flexibility in when you take your daily injection. If your schedule is unpredictable and you sometimes inject a few hours late, Tresiba’s extended duration provides a wider safety margin before coverage drops off.
Premixed Insulin Combinations
Premixed insulins combine a rapid or short-acting insulin with an intermediate-acting one in a fixed ratio. The numbers in the name tell you the percentage of each component. A 70/30 mix, for example, is 70% NPH and 30% rapid or regular insulin.
Common options in the U.S. include:
- Novolin 70/30 and NovoLog Mix 70/30: 70% NPH with 30% regular or rapid-acting insulin
- Humalog Mix 75/25: 75% NPH with 25% insulin lispro
- Humalog Mix 50/50: An even split of NPH and insulin lispro
These are convenient for people who would otherwise need to draw up and inject two separate insulins. The tradeoff is less flexibility. You can’t adjust the mealtime and background doses independently, so if your carb intake varies a lot from meal to meal, separate injections of basal and bolus insulin give you more control.
Concentrated Insulin
Most insulin in the U.S. is sold at a standard concentration of 100 units per milliliter (U-100). Concentrated formulations pack more insulin into a smaller volume, which is useful for people who need large daily doses. Available options include Humalog U-200 (twice the concentration), Tresiba U-200, Toujeo (insulin glargine U-300, three times standard), and Humulin R U-500 (five times standard). These aren’t different “types” of insulin in terms of how they work. They contain the same active ingredient as their U-100 counterparts, just in a more compact dose. The practical benefit is a smaller injection volume, which can be more comfortable and absorb more reliably.
Inhaled Insulin
Afrezza is the only inhaled insulin available. It’s a rapid-acting powder you breathe in through a small inhaler at the start of a meal. Insulin reaches your bloodstream within 12 to 15 minutes after inhalation, and blood sugar effects taper off by about 160 minutes (just under 3 hours). That shorter duration compared to injected rapid-acting insulin can be an advantage for people prone to low blood sugar between meals, since the insulin clears out faster. It’s approved for adults with type 1 or type 2 diabetes, though it isn’t recommended for anyone who smokes or has chronic lung conditions like asthma or COPD.
What’s on the Horizon
A once-weekly insulin called icodec is currently in late-stage clinical trials. It has a half-life of approximately one week, meaning a single injection could replace seven daily basal insulin shots. Phase 3 trials have tested it in both type 1 and type 2 diabetes. If approved, it would be the first insulin to offer weekly dosing, a significant shift for the millions of people who currently inject long-acting insulin every day.