Insulin
Also known as: Insulin glargine, Insulin detemir, Insulin degludec, Insulin icodec, Insulin aspart, Insulin lispro, Insulin glulisine, Regular insulin (R), NPH insulin, Humulin, Novolin, Lantus, Basaglar, Toujeo, Levemir, Tresiba, Awiqli, Humalog, NovoLog, NovoRapid, Apidra, Fiasp, Lyumjev
Pancreatic hormone / antidiabetic agent
What it is
Insulin is used by people with type 1 diabetes (who require it for survival) and many people with type 2 diabetes to control blood sugar. It lowers glucose by helping cells absorb it for energy. Different formulations — rapid-acting, long-acting, and once-weekly — let clinicians and patients tailor treatment to individual needs.
The scientific side
insulin exerts its primary metabolic effects by binding to the insulin receptor (IR), a tyrosine kinase receptor expressed on skeletal muscle, adipose tissue, and liver. Receptor binding triggers autophosphorylation and downstream activation of the IRS-1/PI3K/Akt signalling cascade, which stimulates translocation of glucose transporter type 4 (GLUT4) to the plasma membrane, thereby facilitating cellular glucose uptake (PMID 42850266). In skeletal muscle, this GLUT4 translocation accounts for the majority of postprandial glucose disposal. In the liver, insulin suppresses hepatic glucose production (glycogenolysis and gluconeogenesis) and promotes glycogen synthesis. In adipose tissue, insulin inhibits lipolysis, reducing circulating free fatty acids. Physiologically, the pancreatic beta cells release insulin in a biphasic pattern — an early first-phase spike within minutes of a glucose stimulus, followed by a sustained second-phase secretion. In type 1 diabetes (T1D), autoimmune destruction of beta cells eliminates endogenous insulin entirely, creating absolute insulin dependence (PMID 41697686). In type 2 diabetes (T2D), relative insulin deficiency combined with peripheral insulin resistance means many patients eventually require exogenous supplementation. Exogenous insulin formulations are engineered to replicate physiological patterns. Long-acting (basal) analogues such as glargine, detemir, and degludec provide flat, peakless background coverage over 18–42 hours, while the investigational once-weekly icodec achieves steady-state coverage over seven days by binding reversibly to albumin (PMID 40937414). Rapid-acting prandial analogues (aspart, lispro, glulisine) are absorbed within 10–15 minutes to blunt post-meal glucose excursions. Ultra-rapid formulations (Fiasp) achieve even faster absorption via excipients that accelerate subcutaneous dispersion (PMID 39643003). Automated insulin delivery (AID) systems close the loop by coupling continuous glucose monitoring to algorithmic pump control, adjusting basal infusion rates in real time to maintain glucose in the 70–180 mg/dL target range without user input (PMID 41788003, PMID 41677018).
Class: Pancreatic hormone / antidiabetic agent
Administration & storage
- Administration
- Subcutaneous injection via insulin pen (most common in outpatient studies; PMID 40033680)Subcutaneous injection via syringe and needle (reported in low-resource settings; PMID 40033680)Continuous subcutaneous insulin infusion (CSII) via insulin pumpincluding hybrid AID systems (PMID 41677018PMID 41788003)Intravenous infusion of regular insulin for critical care / surgical hyperglycaemia managementIntranasal insulin (exploratory; ClinicalTrials NCT01767909)
- Storage
- Unopened vials and pens: refrigerated at 2–8°C; do not freeze. After first use: most formulations stable at room temperature (<25–30°C) for 28–56 days depending on product (check individual prescribing information). Insulin pens/cartridges in use should be stored at room temperature and not returned to the refrigerator. Protect all formulations from direct sunlight and heat. Discard if solution is cloudy, discoloured, or contains particulates (except NPH/premixed suspensions).
- Cautions
- Hypoglycaemia is the most common and potentially life-threatening adverse effect; all patients must be counselled on recognition and treatment (fast-acting glucose, glucagon kit for severe episodes) (PMID 42155411, PMID 40186685),Dose errors due to insulin concentration confusion (U-100 vs U-200 vs U-300 vs U-500) can cause 2–5× overdose; use product-matched pens and syringes only,Physical activity increases glucose consumption and can precipitate hypoglycaemia; ONWARDS 1-5 post-hoc analysis found no consistent increase in physical activity-attributed hypoglycaemia with once-weekly icodec vs once-daily comparators, though vigilance is warranted (PMID 40186685),Insulin requirements change significantly during illness, surgery, pregnancy, and with addition/removal of other glucose-lowering agents; frequent monitoring and dose adjustment required,Lipohypertrophy at repeated injection sites impairs insulin absorption; systematic site rotation is essential,Allergy and localised injection-site reactions occur rarely with modern analogues but can include erythema, pruritis, and induration,Insulin is prohibited by WADA in sport without a valid TUE; non-diabetic use for anabolic or performance-enhancing purposes carries severe hypoglycaemia risk
Legal & regulatory status
Multiple insulin formulations are FDA-approved for glycemic control in type 1 and type 2 diabetes mellitus. Rapid-acting analogues (aspart, lispro, glulisine, Fiasp, Lyumjev), long-acting analogues (glargine…
Insulin is prohibited in-competition under the World Anti-Doping Agency (WADA) Prohibited List (S4 — Hormone and Metabolic Modulators) when used by athletes without a documented medical diagnosis of insulin-dependent…
Insulin products are approved by Health Canada under the Food and Drugs Act for diabetes management. Biosimilar insulin glargine (Basaglar) and originator products (Lantus, Tresiba, Levemir, Humalog, NovoRapid) hold…
What it's studied for
- Type 1 diabetes mellitus — lifelong insulin replacement Tier 1 — RCT / Guideline
- Type 2 diabetes mellitus — intensification when oral agents insufficient Tier 1 — RCT / Guideline
- Basal-bolus insulin therapy — type 2 diabetes treatment intensification Tier 1 — RCT
- Automated insulin delivery (AID/closed-loop) for type 1 and type 2 diabetes Tier 1 — RCT / Real-world evidence
- Insulin therapy in pregnancy (preexisting diabetes) Tier 1 — Guideline
- Hyperglycaemia management in hospitalised patients Tier 2 — RCT
- Counterregulatory deficiency and hypoglycaemia prevention strategies in T1D Tier 2 — RCT
- Insulin dose reduction in diabetes with comorbid conditions (lipodystrophy, obesity) Tier 2 — Case series / Pilot RCT
Safety signals
- Hypoglycaemia (low blood glucose)
- Nocturnal hypoglycaemia
- Weight gain
- Injection site lipohypertrophy
- Hypokalaemia (low potassium)
- Diabetic ketoacidosis (DKA) from insulin omission or pump failure
- Insulin-associated increased hypoglycaemia risk with physical activity
- Dose concentration errors (U-100 vs U-200 / U-300 / U-500 confusion)
All studies (9)
Frequently asked
What is the difference between basal and bolus insulin?
Basal insulin (e.g., glargine, detemir, degludec) is a long-acting formulation designed to control background blood glucose levels between meals and overnight. Bolus insulin (e.g., aspart, lispro) is rapid-acting and taken just before or with meals to manage the rise in glucose from food. Most people with type 1 diabetes and some with type 2 use both together in a basal-bolus regimen. Your prescriber sets the starting doses and titration schedule for your individual needs.
Is once-weekly insulin as effective as daily insulin?
Clinical trials including ONWARDS and COMBINE 3 found that once-weekly insulin icodec (Awiqli) achieved similar HbA1c reductions to once-daily basal insulins in people with type 2 diabetes. In type 1 diabetes, once-weekly formulations have shown slightly higher hypoglycaemia rates compared with daily degludec, so they are not yet established as a preferred option for T1D. Discuss with your endocrinologist whether a once-weekly formulation is appropriate for your situation.
Can insulin cause weight gain?
Yes, insulin can contribute to modest weight gain (typically 1–4 kg with basal initiation) by promoting glucose storage and reducing urinary glucose loss. However, combining insulin with a GLP-1 receptor agonist (such as in the IcoSema fixed-ratio combination studied in COMBINE 3) substantially offset this effect. If weight gain is a concern, discuss adjunctive therapies with your doctor.
What should I do if my blood sugar drops too low (hypoglycaemia)?
Mild-to-moderate hypoglycaemia (blood glucose <70 mg/dL with symptoms) should be treated immediately with 15–20 g of fast-acting carbohydrates (e.g., glucose tablets, 150–200 mL of fruit juice, or regular soda). Recheck glucose after 15 minutes and repeat if still below 70 mg/dL. Severe hypoglycaemia causing confusion or unconsciousness requires injectable or nasal glucagon and emergency medical assistance. All patients on insulin should have glucagon available at home and ensure people around them know how to use it.
Is insulin safe during pregnancy?
Insulin is the preferred and safest pharmacological treatment for managing blood glucose in pregnant people with pre-existing type 1 or type 2 diabetes. Unlike many oral diabetes medications, insulin does not cross the placenta in clinically significant amounts. A 2025 joint Endocrine Society guideline recommends hybrid closed-loop insulin pump therapy for pregnant people with T1D to improve time-in-range and reduce complications. Insulin requirements change throughout pregnancy and postpartum, requiring close medical supervision.
How should I rotate my injection sites?
Systematic site rotation prevents lipohypertrophy (lumpy fatty tissue) that impairs insulin absorption and can cause unpredictable glucose control. Common injection sites include the abdomen (avoiding the 2-inch ring around the navel), outer thighs, buttocks, and upper arms. Within each anatomical region, move each injection at least 1 cm from the previous one. Avoid injecting into areas where you feel lumps or hard tissue. Your diabetes care team can map out a rotation schedule for your specific regimen.