Insulin Types Chart: Onset, Peak and Duration + Mixing Rules

Quick answer: Insulin types differ in how fast they start, peak and wear off. Rapid-acting (lispro, aspart, glulisine) starts in 10-30 minutes, peaks at about 1 hour and lasts 3-5 hours. Regular starts in 30-60 minutes, peaks at 2-3 hours and lasts 5-8 hours. NPH starts in 1-2 hours, peaks at 4-12 hours and lasts 12-18 hours. Glargine, detemir and degludec are essentially peakless basal insulins (detemir, sold as Levemir, was discontinued in the U.S. at the end of 2024 but still appears in older questions).

Insulin questions almost always hinge on one number: the peak. The peak is when blood glucose drops the hardest. That makes it the window where your patient is most likely to go hypoglycemic, and the time you watch them and feed them most carefully. Rapid-acting insulin peaks in about an hour, regular in 2-3 hours, NPH in 4-12 hours, and the long-acting basal insulins (glargine, detemir, degludec) are essentially peakless. Learn the chart below, learn “clear before cloudy,” and remember that Regular is the insulin you hang as an IV drip.

Insulin types chart: onset, peak, and duration

These are the standard reference values for subcutaneous insulin in an adult. Ranges vary a little by source and by the individual patient, but the numbers below are the defensible, testable values you should commit to memory. The single most important column is the peak, because that is where hypoglycemia lives.

A quick mnemonic for the color cue: rapid and regular insulins are clear; NPH is cloudy because the protamine suspended in it scatters light. Glargine and detemir are also clear, but do not let “clear” trick you into mixing them with anything (more on that below).

How do you read the chart in real life?

Match the insulin to the patient’s needs over the day. Rapid-acting covers the spike from a single meal, so it is given right at the start of eating. Regular covers a meal too but works more slowly, so it is given about 30 minutes before food. NPH and the long-acting insulins are basal, holding glucose down between meals and overnight. Premixed products try to do both jobs in one injection, which is convenient but less flexible.

When will my patient get hypoglycemic? Tie it to the peak

This is the concept the exam tests over and over. Hypoglycemia is most likely at the insulin’s peak, because that is when the most insulin is active and pulling glucose into cells. Your job is to make sure food and monitoring line up with that window.

This table points to two clinical pearls. First, rapid-acting insulin and the meal tray are a package deal: give the insulin only when you can confirm the patient is going to eat. Hold it (and check with the provider) if the patient is NPO, nauseated, or has a tray that may not arrive. Second, bedtime NPH is the usual culprit behind a patient found diaphoretic and confused at 0300; that is the NPH peaking overnight.

What does “peakless” really mean for long-acting insulin?

Glargine, detemir, and degludec release slowly and steadily, so they produce a relatively flat level with no sharp peak. That flat profile is the whole point: it mimics the body’s basal insulin and carries a lower risk of sudden lows. It does not mean zero hypoglycemia risk, especially if the patient skips meals or stacks doses, but there is no single hour you circle on the clock the way you do with NPH. For that reason these are usually dosed once daily, though detemir is dose-dependent and may be ordered twice daily (degludec is forgiving on timing because it lasts over 42 hours).

Insulin mixing rules: clear before cloudy

When a patient needs both a short-acting and an intermediate-acting insulin in one syringe, the only standard combination you mix is Regular + NPH. The rule for drawing them up is clear before cloudy: draw the clear Regular insulin into the syringe first, then the cloudy NPH.

Why clear before cloudy?

If a little of the cloudy NPH (which contains protamine) gets pushed back into the Regular vial, it can contaminate your fast-acting insulin and blunt how quickly it works. Drawing the clear Regular first protects that vial. The full sequence is worth memorizing as a skills-checkoff and an NCLEX ordered-response item:

Keep the two sequences straight: you inject air into the cloudy vial first, but you draw insulin out of the clear vial first. Air goes cloudy-then-clear; insulin comes out clear-then-cloudy. Once the two are mixed in the syringe, administer promptly.

Which insulins must NEVER be mixed?

Glargine and detemir must never be mixed with any other insulin in the same syringe. Glargine is formulated at an acidic pH and precipitates the moment it meets a neutral-pH insulin; detemir depends on binding to albumin for its long action, and mixing disrupts that profile. Either way absorption becomes unpredictable, so they always get their own injection. Premixed products (such as 70/30) are pre-formulated by the manufacturer and are not mixed further at the bedside. Degludec is also given on its own. When in doubt, the safe answer on a test and at the bedside is: do not mix a long-acting basal insulin with anything.

Which insulin can be given IV?

Regular insulin is the insulin given intravenously. It is the insulin used in continuous IV drips for diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state, and it is given as an IV dose for severe hyperkalemia (paired with dextrose to drive potassium into cells). NPH and the long-acting insulins are subcutaneous only — they are suspensions or designed for slow subcutaneous release and would be dangerous given IV. (Rapid-acting analog labels do carry IV dosing instructions for diluted, supervised infusion, but Regular is the standard agent and the expected exam answer.) If a question asks which insulin can hang as a drip, the answer is Regular, every time.

One more high-yield point on administration: insulin is measured in units, drawn up in an insulin syringe, and double-checked by a second nurse per facility policy because it is a high-alert medication. Subcutaneous insulin is given at a 90-degree angle (45 degrees in a very thin patient), and you rotate sites within one anatomic region rather than scattering across the body.

Recognizing and treating hypoglycemia

Because insulin’s peak is a hypoglycemia trigger, you have to know the signs and the fix cold. Early hypoglycemia is adrenergic: shakiness, sweating, tachycardia, hunger, anxiety. As glucose falls further it becomes neuroglycopenic: confusion, slurred speech, seizures, loss of consciousness. The treatment threshold is a blood glucose below 70 mg/dL.

For a conscious patient who can swallow, follow the rule of 15: give 15 grams of fast-acting carbohydrate (4 oz juice, glucose tablets, regular soda), recheck the glucose in 15 minutes, and repeat if it is still below 70. Follow up with a protein-plus-carb snack once the level recovers to prevent a rebound drop. For an unconscious patient or one who cannot safely swallow, give IV dextrose (D50) if there is IV access, or IM/subcutaneous glucagon if there is not. Never pour food or fluid into the mouth of someone who is not alert.

For a fuller walk-through of diabetes, DKA, and the rest of the hormones, work through our NCLEX endocrine review. And because insulin is a high-alert drug, it pairs naturally with our therapeutic drug levels and toxicity guide, which covers the other medications you have to monitor by the numbers.

Sample NCLEX insulin questions

Frequently Asked Questions

What is the most important thing to know about insulin for the NCLEX?

The peak. The peak is when blood glucose drops most sharply and when hypoglycemia is most likely, so it drives your monitoring and your meal timing. If you know that rapid-acting peaks around 1 hour, regular at 2-3 hours, and NPH at 4-12 hours, you can answer most “when will hypoglycemia occur” and “when should the client eat” questions correctly.

Which insulins are clear and which are cloudy?

Rapid-acting (lispro, aspart, glulisine), Regular, glargine, and detemir are all clear. NPH is the cloudy one because it contains protamine in suspension. When mixing Regular with NPH, the rule “clear before cloudy” means you draw up the clear Regular before the cloudy NPH. Note that glargine and detemir are clear but are never mixed with anything.

Can you mix any two insulins together?

The standard mixable combination is Regular plus NPH, drawn clear before cloudy. Rapid-acting insulin may also be mixed with NPH if ordered, drawing the rapid insulin first and giving the mix immediately. Glargine, detemir, and degludec are never mixed with another insulin in the same syringe, and premixed products are not combined further.

Which insulin can be given IV?

Regular insulin — it is the standard agent and the expected exam answer. It is the insulin used in continuous IV infusions for diabetic ketoacidosis, hyperosmolar hyperglycemic state, and as part of the treatment for severe hyperkalemia with dextrose. NPH and the long-acting basal insulins are subcutaneous only.

Why is long-acting insulin called “peakless”?

Glargine, detemir, and degludec release at a slow, steady rate that produces a relatively flat blood level with no sharp spike. That flat profile mimics the body’s basal insulin secretion and carries a lower risk of sudden hypoglycemia. There is no single peak hour to plan a feeding around, which is why these are typically dosed once daily — though detemir may be ordered twice daily.

Want to lock these numbers in until they are automatic? Practice free NCLEX questions with full rationales for every answer choice, right and wrong, no credit card required.