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approvedWeight Loss & Diabetes

Insulin

Also known as: Human Insulin, Regular Insulin, Humulin, Novolin, Insulin (rDNA origin)

Insulin is a 51-amino-acid peptide hormone produced by the beta cells of the pancreatic islets of Langerhans. It consists of two chains (A-chain: 21 amino acids, B-chain: 30 amino acids) linked by disulfide bonds. First isolated by Banting and Best in 1921 and approved for human use in 1922, insulin is arguably the most important peptide drug in medical history, saving millions of lives from type 1 diabetes. It is the master regulator of glucose metabolism, promoting cellular glucose uptake, glycogen synthesis, lipogenesis, and protein synthesis while inhibiting gluconeogenesis, glycogenolysis, and lipolysis.

3 cited references·5 researched benefits

Quick Answer

Insulin is a 51-amino-acid peptide hormone produced by pancreatic beta cells that serves as the body's primary regulator of blood glucose. Discovered in 1921 and the first peptide drug ever approved, it remains essential therapy for type 1 diabetes and advanced type 2 diabetes. Modern insulin analogs include rapid-acting (lispro, aspart), long-acting (glargine, degludec), and ultra-rapid formulations that collectively represent the most widely used peptide drug class worldwide, with a global market exceeding $30 billion.

Key Facts

Mechanism
Insulin binds to the insulin receptor (IR), a receptor tyrosine kinase expressed on virtually all mammalian cells. Binding triggers autophosphorylation of the IR beta subunits, activating the IRS-1/PI3K/Akt signaling cascade. In muscle and adipose tissue, this promotes translocation of GLUT4 glucose transporters to the cell surface, enabling glucose uptake. In the liver, insulin activates glycogen synthase (promoting glycogen storage), stimulates lipogenesis, and suppresses gluconeogenesis and glycogenolysis. In muscle, it promotes amino acid uptake and protein synthesis. Insulin also activates the MAPK/ERK pathway, promoting cell growth and differentiation. It has a profound anabolic effect across multiple tissue types.
Research Status
approved
Half-Life
~5–6 minutes (endogenous; analog half-lives vary from minutes to >24 hours)
Molecular Formula
C₂₅₇H₃₈₃N₆₅O₇₇S₆
Primary Use
Weight Loss & Diabetes
Table of Contents

Benefits

  • Life-saving treatment for type 1 diabetes — replaces absent endogenous insulin productionstrong
  • Essential glycemic control in advanced type 2 diabetes when oral agents are insufficientstrong
  • Reduction in diabetic complications (retinopathy, nephropathy, neuropathy) with intensive glucose controlstrong
  • Potent anabolic effects — promotes protein synthesis and muscle glucose uptake during exercise recoverystrong
  • Emergency treatment for diabetic ketoacidosis (DKA) and hyperglycemic hyperosmolar statestrong

Dosage Protocols

RouteDosage RangeFrequencyNotes
Subcutaneous injection (Basal)10–80 units/day (highly individualized)Once or twice dailyLong-acting analogs (glargine, detemir, degludec) provide 24-hour basal coverage. Starting dose typically 10 units or 0.1–0.2 units/kg, titrated to fasting glucose targets.
Subcutaneous injection (Bolus/Prandial)2–20 units per meal (carb ratio-based)Before each mealRapid-acting analogs (lispro, aspart, glulisine) cover mealtime glucose. Dosed using insulin-to-carb ratios (typically 1 unit per 10–15g carbs) plus correction factor.
Intravenous infusion (Hospital)0.1 units/kg/hrContinuous infusionUsed for DKA, hyperglycemic emergencies, and perioperative glucose management. Only regular insulin (not analogs) is used intravenously.

Medical disclaimer

Dosage information is provided for educational reference only. Always follow your prescriber's instructions and consult a qualified healthcare provider before starting any peptide protocol.

Side Effects

  • Hypoglycemia — the most common and potentially dangerous side effect, ranging from mild shakiness to seizures and comaserious
  • Weight gain — insulin promotes lipogenesis and reduces glycosuria, typically 2–4 kg with initiationcommon
  • Injection site lipodystrophy — lipohypertrophy (fatty lumps) or lipoatrophy at frequently used injection sitescommon
  • Hypokalemia — insulin drives potassium into cells, which can lower serum potassium to dangerous levelsserious
  • Allergic reactions — rare with modern recombinant human insulin analogs but possiblerare

Frequently Asked Questions

Why is insulin considered a peptide?
Insulin is a 51-amino-acid peptide hormone composed of two polypeptide chains (A-chain with 21 amino acids and B-chain with 30 amino acids) connected by two inter-chain disulfide bonds and one intra-chain disulfide bond. It is synthesized as a single preproinsulin precursor, which is processed to proinsulin and then cleaved to release the mature insulin molecule and C-peptide. As a naturally occurring peptide hormone, it is the prototypical peptide drug and the first to be used therapeutically, predating all other peptide therapeutics by decades.
What are the different types of insulin analogs?
Modern insulin analogs are engineered modifications of human insulin designed to alter absorption kinetics. Rapid-acting analogs (lispro, aspart, glulisine) have amino acid swaps that prevent hexamer formation, allowing faster absorption (onset 15 minutes, peak 1–2 hours). Long-acting analogs (glargine, detemir, degludec) have modifications that create slow-release depots (glargine microprecipitates, detemir binds albumin, degludec forms multi-hexamer chains). Ultra-rapid analogs (faster aspart, URLi lispro) add excipients for even quicker absorption. Premixed formulations combine rapid and intermediate insulin.
Can insulin be used for bodybuilding or muscle growth?
Insulin is a potent anabolic hormone that promotes amino acid uptake and protein synthesis in muscle. Some bodybuilders use exogenous insulin to enhance nutrient partitioning and muscle growth, typically in combination with growth hormone and anabolic steroids. This practice is extremely dangerous — insulin-induced hypoglycemia can cause seizures, brain damage, and death within minutes. Unlike most performance-enhancing drugs, the margin between an "effective" and lethal dose of insulin is very narrow. Multiple bodybuilder deaths have been attributed to insulin misuse. This is not recommended.
How has insulin therapy evolved since 1922?
The evolution of insulin is one of medicine's greatest stories. The first insulins (1922) were crude animal pancreas extracts. Purified animal insulins (pork, beef) dominated through the 1970s. Recombinant human insulin (Humulin) was introduced in 1982 as the first commercially available recombinant DNA pharmaceutical product. Rapid-acting analogs arrived in the 1990s (lispro 1996, aspart 2000), long-acting in the 2000s (glargine 2000, degludec 2013). Modern delivery has evolved from glass syringes to pen devices, insulin pumps, and closed-loop "artificial pancreas" systems. Oral and inhaled insulin formulations are also available.

References

  1. 1
    Insulin: discovery, structure, and role in the management of diabetes mellitus — a historical perspective(2005)PubMed ↗
  2. 2
    Insulin analogs: pharmacokinetic profiles and clinical outcomes in type 1 and type 2 diabetes(2015)PubMed ↗
  3. 3
    The DCCT/EDIC Study: intensive insulin therapy and long-term complications of type 1 diabetes(2014)PubMed ↗

Latest Research

Last updated: 2026-02-19