Insulin aspart
Human insulin with one amino acid changed, so it acts faster at meals: approved since 2000, reformulated as Fiasp in 2017, and now made by biosimilar manufacturers
Insulin aspart is human insulin with the proline at position 28 of the B chain replaced by aspartic acid. After an injection under the skin it reaches its peak concentration in 40 to 50 minutes, against 80 to 120 minutes for regular human insulin, so it is taken 5 to 10 minutes before a meal. Novo Nordisk's NovoLog was approved in the US in 2000; Fiasp, the same insulin with two added excipients, acts faster still. It is a prescription medicine, and its main risk, like every insulin's, is low blood sugar.
What is it?
Regular human insulin injected under the skin takes an hour or two to reach its peak, so it has to be given well before a meal and lingers after it. Insulin aspart changes one amino acid, replacing the proline at position 28 of the B chain with aspartic acid. The result is absorbed faster: in the studies behind its US label its median time to peak concentration was 40 to 50 minutes, against 80 to 120 minutes for regular human insulin, and it is injected 5 to 10 minutes before a meal. Early trials found smaller rises in blood sugar after meals and, in type 1 diabetes, fewer hypoglycaemic events than with human insulin.
FDA approved Novo Nordisk's NovoLog on June 7, 2000; it is sold elsewhere as NovoRapid. Its label covers adults and children with diabetes, by injection under the skin, by insulin pump and intravenously under medical supervision. On September 29, 2017 FDA approved Fiasp, the same insulin with niacinamide and L-arginine added. In clinical pharmacology studies Fiasp appeared in the blood within about three minutes, doubled early exposure and gave up to 2.5 times the glucose-lowering effect of standard insulin aspart in the first 30 minutes, with an earlier offset.
Trials have since compared the two formulations where timing matters most. In pregnancy, 216 women with type 1 or type 2 diabetes randomised to Fiasp or insulin aspart had babies of similar birthweight and similar HbA1c. In hospitalised adults with type 2 diabetes, Fiasp kept blood sugar in range for more of the four hours after meals (45% against 36%). In children aged 2 to 6 on an automated insulin delivery system, the two performed the same.
Insulin aspart is now made by other companies too. FDA approved the biosimilars Merilog on February 14, 2025, Kirsty on July 15, 2025 and Garzulys on July 24, 2026. Their trials compared them with the original: similar rates of pump infusion-set occlusion in a crossover study, and equivalent antibody responses and blood-sugar control in a 24-week trial of 478 patients with type 1 diabetes. Like every insulin, insulin aspart's commonest serious risk is hypoglycaemia; its label also warns of low potassium, allergic reactions and fluid retention with thiazolidinediones.
Mechanism of Action
Insulin aspart acts on the insulin receptor exactly as human insulin does. What changed is how quickly it gets there after an injection.
The insulin receptor
Like human insulin it lowers blood glucose by stimulating glucose uptake into muscle and fat and suppressing glucose production by the liver. In glucose-clamp studies in healthy people, the glucose infusion needed to hold blood sugar steady rose higher and peaked earlier than with human insulin.
Faster absorption from under the skin
Replacing proline B28 with aspartic acid speeds absorption: higher serum insulin concentrations are reached sooner after injection, and they also fall faster, which shortens the tail that causes hypoglycaemia between meals and at night.
Fiasp: faster still
Adding niacinamide and L-arginine accelerates initial absorption. Onset of appearance in blood is about 3 minutes, time to peak about 55 minutes, early exposure is about 25% lower from the thigh than from the abdomen or arm, and absolute bioavailability is about 80%.
Pumps and automated delivery
Given by pump, Fiasp switched on 11 minutes sooner and off 24 minutes sooner than standard insulin aspart, with more than twice the insulin action in the first 30 minutes; in young children on a closed-loop system, glucose outcomes were the same with either.
Published Research
These are studies of insulin aspart read from their PubMed abstracts: the reviews of its pharmacology, trials of the faster Fiasp formulation in pregnancy, hospital care and young children, and trials of the biosimilars. The drug's original approval trials are summarised in the reviews rather than carded one by one.
Early pharmacology against human insulin
After subcutaneous injection of 0.15 to 0.2 U/kg, insulin aspart reached higher serum concentrations sooner than human insulin and fell faster; glucose infusion rates in clamp studies were higher and peaked earlier. In type 1 diabetes, rises in glucose after meals were smaller, night-time lows were less deep, and hypoglycaemic events were generally less frequent than with human insulin.
The drug at six years
Insulin aspart is absorbed faster and reaches higher plasma concentrations than soluble human insulin, giving better control of glucose after meals; its shorter action makes hypoglycaemia between meals and at night less of a problem. The review notes approval for continuous subcutaneous infusion and its use in pregnancy.
Pharmacology of faster aspart
Faster aspart adds niacinamide and L-arginine to insulin aspart. It appears in the bloodstream earlier and lowers glucose more within the first 30 minutes; given by pump it switched on 11 minutes and off 24 minutes sooner, with more than 100% greater insulin action in the first 30 minutes. Tolerability and pump compatibility were similar to standard insulin aspart.
Faster aspart: pharmacokinetics and clinical consequences
Across clinical pharmacology trials in type 1 and type 2 diabetes, faster aspart's concentration and glucose-lowering profiles were shifted earlier than insulin aspart's, with earlier onset, doubled initial exposure and up to a 2.5-fold greater glucose-lowering effect in the first 30 minutes, and earlier offset; results were consistent in the elderly, children, adolescents and Japanese people, and by pump.
Faster aspart in different injection sites
In 21 healthy men, onset of appearance (about 3 minutes), time to half-maximum (about 20 minutes) and time to peak (about 55 minutes) were similar after injection into the abdomen, upper arm or thigh. Early exposure and peak concentration were about 25% lower from the thigh, total exposure was similar, and absolute bioavailability was about 80%.
Pregnancy: faster aspart against insulin aspart
In an open-label trial in Copenhagen, 216 women with type 1 or type 2 diabetes were randomised in early pregnancy and followed until three months after delivery. Infant birthweight SD score was 1.0 with faster aspart and 1.2 with insulin aspart (difference -0.22; P=0.23), HbA1c at 33 weeks was 42 against 43 mmol/mol, and no additional safety issues were seen.
Hospitalised adults with type 2 diabetes
137 non-critically ill patients on bedtime glargine were randomised to Fiasp or insulin aspart for meal and correction doses in a safety-net hospital. Time in the 100 to 180 mg/dL range over the four hours after meals was 45% on Fiasp and 36% on insulin aspart (P=0.012), meeting the prespecified non-inferiority criterion.
Very young children on a closed-loop system
In a double-blind crossover trial, 25 children aged 2 to 6 with type 1 diabetes used the CamAPS FX hybrid closed-loop system with Fiasp or standard insulin aspart for eight weeks each. Time in range was 64% against 65% (difference -0.33%; P=0.71), time below 3.9 mmol/L did not differ, and there was no severe hypoglycaemia or ketoacidosis.
A biosimilar in insulin pumps
In a randomised crossover study of 45 adults with type 1 diabetes, four weeks each of the biosimilar SAR341402 and originator NovoLog by pump gave similar numbers of people with at least one infusion-set occlusion (14 of 43 against 12 of 43; risk difference 4.1%, 95% CI -9.3% to 17.4%).
Biosimilar MYL-1601D: 24 weeks, 478 patients
In an open-label phase 3 trial in type 1 diabetes, mealtime MYL-1601D or US reference insulin aspart was combined with once-daily glargine. The rate of treatment-emergent antibody responses met the prespecified equivalence margin of ±11.7%, and HbA1c, fasting glucose, insulin doses and adverse events including hypoglycaemia were compared between the groups.
Insulin aspart-szjj (Merilog), a biosimilar
Insulin aspart-szjj is approved for the same indication as the reference product. Its physicochemical characteristics were similar, pharmacokinetic and pharmacodynamic equivalence was shown in type 1 diabetes, and its efficacy, tolerability, safety and immunogenicity were similar to reference insulin aspart in type 1 and type 2 diabetes.
Dosing Data
Insulin aspart is dosed by the prescriber for each patient, usually alongside a longer-acting insulin. The label sets how it is given, not how much.
Educational information, not medical advice. Each dose above is tagged with its source: an approved label, a published human study, animal data, or amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.
Side Effects & Contraindications
Reported Side Effects
From the NovoLog label and the trials above.
Contraindications & Cautions
From the prescribing information; a clinician decides.
Legal Status
Insulin aspart is an approved prescription medicine in the US and the EU.
Frequently Asked Questions
?How fast does insulin aspart work?
In the studies behind its label, it reached peak concentration 40 to 50 minutes after an injection under the skin, against 80 to 120 minutes for regular human insulin, which is why it is taken 5 to 10 minutes before a meal.
?What is the difference between NovoLog and Fiasp?
Both are insulin aspart. Fiasp adds niacinamide and L-arginine, which speed initial absorption: it appears in the blood within about three minutes and has up to 2.5 times the glucose-lowering effect of standard insulin aspart in the first 30 minutes.
?Is there a biosimilar insulin aspart?
Yes. FDA approved Merilog in February 2025, Kirsty in July 2025 and Garzulys in July 2026. Their trials found them equivalent to the original on antibody responses and glucose control.
?Can insulin aspart be used in pregnancy?
Its reviews describe it as a treatment option during pregnancy, and in a 2023 trial of 216 pregnant women with diabetes, Fiasp and standard insulin aspart gave similar infant birthweights and HbA1c. Treatment in pregnancy is managed by the care team.
?What is its main side effect?
Low blood sugar, which is the most common adverse reaction with any insulin. The label also warns of low potassium, severe allergic reactions and fluid retention when combined with thiazolidinediones.
?Why is an insulin on a peptide site?
Insulin is a peptide hormone of two chains, and insulin aspart is one of the most widely used peptide medicines. It sits here beside the other insulins and GLP-1 drugs so their evidence can be compared.
References
- [fda-pi] Novo Nordisk. NOVOLOG (insulin aspart) injection, US prescribing information: B28 proline-to-aspartic acid substitution, formula C256H381N65O79S6 and molecular weight 5825.8 Da (section 11); median time to peak 40 to 50 minutes vs 80 to 120 for regular human insulin and apparent half-life 81 minutes (section 12.3); hypoglycemia, hypokalemia, hypersensitivity and TZD fluid retention (section 5). DailyMed version effective February 28, 2023, read September 30, 2026.
- [pubmed] Simpson KL, et al. "Insulin aspart." Drugs, 1999;57(5):759-65; discussion 766-7. PMID: 10353301.
- [pubmed] Owens D, et al. "Insulin aspart: a review." Expert Opin Drug Metab Toxicol, 2006;2(5):793-804. PMID: 17014395.
- [pubmed] Biester T, et al. "Pharmacological Properties of Faster-Acting Insulin Aspart." Curr Diab Rep, 2017;17(11):101. PMID: 28940145.
- [pubmed] Haahr H, et al. "Fast-Acting Insulin Aspart: A Review of its Pharmacokinetic and Pharmacodynamic Properties and the Clinical Consequences." Clin Pharmacokinet, 2020;59(2):155-172. PMID: 31667789.
- [pubmed] Hövelmann U, et al. "Pharmacokinetic Properties of Fast-Acting Insulin Aspart Administered in Different Subcutaneous Injection Regions." Clin Drug Investig, 2017;37(5):503-509. PMID: 28185141.
- [pubmed] Nørgaard SK, et al. "Faster-acting insulin aspart versus insulin aspart in the treatment of type 1 or type 2 diabetes during pregnancy and post-delivery (CopenFast): an open-label, single-centre, randomised controlled trial." Lancet Diabetes Endocrinol, 2023;11(11):811-821. PMID: 37804858.
- [pubmed] Alexanian SM, et al. "Comparing Postprandial Glycemic Control Using Fiasp vs Insulin Aspart in Hospitalized Patients With Type 2 Diabetes." Endocr Pract, 2025;31(3):306-314. PMID: 39643003.
- [pubmed] Ware J, et al. "Hybrid Closed-Loop with Faster Insulin Aspart Compared with Standard Insulin Aspart in Very Young Children with Type 1 Diabetes: A Double-Blind, Multicenter, Randomized, Crossover Study." Diabetes Technol Ther, 2023;25(6):431-436. PMID: 36880866.
- [pubmed] Thrasher J, et al. "Safety and Tolerability of Insulin Aspart Biosimilar SAR341402 Versus Originator Insulin Aspart (NovoLog) When Used in Insulin Pumps in Adults with Type 1 Diabetes: A Randomized, Open-Label Clinical Trial." Diabetes Technol Ther, 2020;22(9):666-673. PMID: 31833801.
- [pubmed] Blevins TC, et al. "Immunogenicity, Efficacy, and Safety of Biosimilar Insulin Aspart (MYL-1601D) Compared with Originator Insulin Aspart (Novolog(®)) in Patients with Type 1 Diabetes After 24 Weeks: A Randomized Open-Label Study." BioDrugs, 2022;36(6):761-772. PMID: 36114990.
- [pubmed] McGuigan A. "Insulin Aspart-szjj: An Insulin Aspart Biosimilar." Clin Drug Investig, 2026;46(3):353-357. PMID: 41572097.
- [pubmed] Brange J, et al. "Monomeric insulins obtained by protein engineering and their medical implications." Nature, 1988;333(6174):679-82. PMID: 3287182.
- [fda] FDA. Drugs@FDA (openFDA): NovoLog BLA 020986 (approved June 7, 2000), Fiasp BLA 208751 (September 29, 2017), Merilog BLA 761325 (February 14, 2025), Kirsty BLA 761188 (July 15, 2025), Garzulys BLA 761497 (July 24, 2026). Read September 30, 2026.
- [other] European Medicines Agency. Medicines register (centrally authorised human medicines): NovoRapid, Fiasp, Kirsty, Insulin aspart Sanofi, Dazparda and Maapliv authorised. Read September 30, 2026.
Sources & Citations
Every study on this page was read from its PubMed record. Approval dates come from FDA's Drugs@FDA database and EMA's register; the pharmacokinetics and warnings come from the NovoLog label on DailyMed. Grey Peptides sells nothing and links to no vendor.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Talk to a licensed clinician about your own situation.