Section 01
What it's used for
Type 1 Diabetes (Approved)
Insulin is essential for survival in type 1 diabetes and cannot be replaced by anything else. Modern treatment uses either several daily injections or a continuous under-the-skin insulin pump to manage blood sugar.
▸Clinical wording
Insulin is essential for survival in type 1 diabetes and remains irreplaceable. Modern management uses multiple daily injections or continuous subcutaneous insulin infusion (pump therapy).
Type 2 Diabetes (Approved)
Insulin is used when oral drugs and GLP-1 receptor agonists fail to control blood sugar. A long-acting background insulin (glargine, detemir, degludec) is usually added first, with mealtime insulin for advanced disease.
▸Clinical wording
Used when oral agents and GLP-1RAs fail to achieve glycemic control. Basal insulin (glargine, detemir, degludec) is typically added first, with bolus insulin for advanced disease.
Smart Insulin Research
Researchers want a glucose-responsive 'smart' insulin. The only version tested in people, MK-2640, was stopped after a 2019 phase 1 trial for being 25-fold weaker than natural insulin. Others remain in lab or animal testing only.
▸Clinical wording
Glucose-responsive "smart" insulin formulations that would automatically adjust activity based on blood glucose have been an active research goal. The only such compound to reach human testing, MK-2640, was discontinued after a phase 1 trial in 2019 because its potency was roughly 25-fold lower than native insulin; other candidates described in the literature remain preclinical, so no glucose-responsive insulin is currently in active clinical-stage development.
Artificial Pancreas Systems
Automated insulin-delivery systems that pair a continuous glucose monitor with an insulin pump are considered the leading edge of diabetes technology, automatically adjusting insulin based on real-time blood sugar readings.
▸Clinical wording
Automated insulin delivery systems coupling continuous glucose monitors with insulin pumps represent the frontier of diabetes technology.
Section 02
Mechanism of Action
The first step at the cell surface
- Insulin binding makes its receptor tag itself, starting the signal inside the cell.
- Adaptor proteins then dock and convert that tag into a lipid-based signal.
- In mice, deleting both adaptors in muscle or liver was as damaging as deleting the receptor.
- Two receptor versions exist, and hybrid receptors prefer growth factors over insulin itself.
▸Clinical wording
Insulin receptor autophosphorylation and IRS docking
The insulin receptor is a tyrosine kinase that autophosphorylates on ligand binding; the IRS family of adaptors then convert that tyrosine phosphorylation signal into a lipid kinase signal by recruiting PI3K (Haeusler 2018). The adaptors are not redundant scaffolding: muscle-specific or liver-specific deletion of both Irs1 and Irs2 in mice phenocopies deletion of the receptor gene itself (Petersen 2018). Two receptor isoforms exist. IR-B expression is highest in liver, while IR-A binds IGF-2 with affinity comparable to insulin, and IR/IGF1R hybrid heterotetramers bind IGF-1 and IGF-2 preferentially over insulin (Boucher 2014).
The central switch for blood sugar
- A lipid signal at the membrane recruits enzymes that switch on the central relay AKT.
- Of the relay's three versions, one handles blood sugar, one growth, one brain development.
- Responses are staged in time: seconds for some targets, minutes for others, hours for fat genes.
- Several brake proteins strip the tags or block the adaptors, keeping the signal in check.
▸Clinical wording
PI3K to PDK1 and AKT2, the metabolic signalling node
PI3K generates PtdIns(3,4,5)P3 at the plasma membrane, recruiting PDK1, which phosphorylates AKT at Thr308; mTORC2 adds the Ser473 site (Haeusler 2018). Of the three AKT isoforms, AKT2 is described as the most important for glucose homeostasis, AKT1 for growth, AKT3 for brain development. Phosphorylation is tiered in time: AKT, TBC1D4 and FOXO respond within seconds, GSK3, TSC2 and S6K within minutes, SREBP1c over hours. The same review catalogues the brakes: PTEN and SHIP2 degrade PIP3, PTP1B, PHLPP and PP2A remove phosphate, and GRB10/GRB14 act as pseudosubstrates blocking IRS access to the receptor kinase domain.
Moving sugar doors to the surface
- In resting fat and muscle cells the sugar transporter sits in tiny storage bubbles.
- The relay switches off a brake, letting those bubbles travel out to the cell surface.
- About half the transporter moves, enough to explain the measured change in sugar transport.
- Knock-in mice cast doubt on how much the glycogen storage step actually contributes.
▸Clinical wording
TBC1D4-Rab control of GLUT4 and glycogen storage
In basal fat and muscle cells most GLUT4 sits in roughly 70 nm tubulo-vesicular storage vesicles clustered near the trans-Golgi network. AKT phosphorylation of TBC1D4/AS160 recruits 14-3-3 and inactivates its Rab-GAP activity, permitting GTP loading of Rab10 in adipocytes; adipose-specific Rab10 knockout in mice blunts insulin-stimulated uptake, whereas in L6 myocytes Rab8a and Rab13 dominate (Klip 2019). About 50% of GLUT4 redistributes to the plasma membrane, enough to account for the measured transport change. AKT also inactivates GSK3, permitting glycogen synthase activation, though GSK3 Ser21/Ser9-to-alanine knock-in mice cast doubt on how much that step contributes (Petersen 2018).
Two ways of switching off liver sugar
- The relay tags a control protein, pushing it out of the nucleus and silencing sugar-making genes.
- Mice without that liver protein run low blood sugar and make less glucose.
- In parallel, insulin blocks fat release from fat tissue by degrading a signalling messenger.
- Less fat reaching the liver is the main brake, since infusing fat abolished the effect.
▸Clinical wording
FOXO1 and the indirect adipose route to hepatic glucose output
AKT phosphorylates FOXO1 at Thr24, Ser256 and Ser319, driving 14-3-3 binding and nuclear exclusion and switching off G6pc and Pck1; mice lacking hepatic FOXO1 show fasting hypoglycaemia and decreased glucose production (Petersen 2018). In liver in vivo, FOXO phosphorylation is maximal within 30 seconds (Haeusler 2018). In parallel, insulin activates adipocyte phosphodiesterase 3B, degrading cAMP and blunting PKA phosphorylation of hormone-sensitive lipase and perilipin. Acute suppression of gluconeogenic flux is largely indirect: less NEFA delivery lowers hepatic acetyl-CoA, an allosteric activator of pyruvate carboxylase, and NEFA infusion during pancreatic clamps abolished the effect.
Building proteins and driving cell division
- One branch releases a growth switch that raises protein production and fat-making genes.
- A second branch, independent of the first, drives a cascade ending in cell multiplication.
- That branch also regulates gene activity and reshaping of the cell's internal skeleton.
- This is why insulin is described as a metabolic and a growth-promoting hormone at once.
▸Clinical wording
mTORC1 protein synthesis and the Ras-ERK mitogenic branch
AKT phosphorylates and inactivates TSC2, releasing mTORC1, which inhibits 4E-BP1 and activates the ribosomal S6 kinases S6K1 and S6K2 to raise translation, and which also feeds SREBP1 and the hepatic lipogenic gene programme (Boucher 2014; Haeusler 2018). A second, PI3K-independent arm runs through Shc and Grb2, whose SH3 domains bind SOS and Gab-1 to load Ras. The resulting ERK1/2 activity plays a direct role in cell proliferation or differentiation, regulating gene expression or extra-nuclear events such as cytoskeletal reorganisation (Boucher 2014). This branch is why insulin signalling is described as metabolic and mitogenic at once.
Section 03
Biological Pathways
- IR/IRS/PI3K/Akt signalingThe insulin receptor autophosphorylates and IRS adaptors convert that signal into PI3K activity; PI3K generates PIP3, recruiting PDK1 to phosphorylate Akt, with AKT2 the isoform key to glucose homeostasis.
- Akt/TBC1D4/GLUT4 and GSK-3βAkt phosphorylates TBC1D4/AS160, inactivating its Rab-GAP activity so GLUT4 moves from storage vesicles to the plasma membrane; Akt also inactivates GSK-3β, permitting glycogen synthase activation.
- Akt/FOXO1 gluconeogenesis suppressionAkt phosphorylates FOXO1, driving nuclear exclusion that switches off the gluconeogenic genes G6pc and Pck1; suppression is also indirect, as blocked adipocyte lipolysis lowers NEFA and hepatic acetyl-CoA.
- mTORC1/p70S6K protein synthesisAkt inactivates TSC2, releasing mTORC1 to inhibit 4E-BP1 and activate ribosomal kinases S6K1 and S6K2, raising translation, while the same node feeds SREBP-1c and hepatic lipogenic genes.
- Ras/Raf/MEK/ERK growth armA PI3K-independent branch runs through Shc and Grb2, whose SH3 domains bind SOS and Gab-1 to load Ras; the resulting ERK1/2 activity drives cell proliferation, making insulin signaling mitogenic too.
Section 04
Dosage Information
A-chain (21 aa) + B-chain (30 aa) linked by 2 disulfide bonds; A: GIVEQCCTSICSLYQLENYCN, B: FVNQHLCGSHLVEALYLVCGERGFFYTPKT| Route / system | Context | Range studied | Limitation |
|---|---|---|---|
| Subcutaneous — type 1 diabetes | ADA Standards of Care, background plus meal insulin | 0.4–1.0 units/kg a day, usually 0.5 in a stable adult — about 35–45 units a day at 70–90 kg, half background and half with meals | A starting estimate, not a range: a doctor resets it per person from measured sugar within days. A “U” read as zero has caused fatal ten-fold overdoses. |
| Subcutaneous — type 2 diabetes | ADA Standards of Care, starting background insulin | 10 units a day or 0.1–0.2 units/kg a day — about 7–18 units at 70–90 kg — raised by 2–4 units or 10–15% a week against fasting sugar | Too low to work on purpose — it is meant to be raised gradually. Above 0.5 units/kg a day it stops lowering average sugar and brings weight gain and low sugar. |
| Intravenous — hospital, ketoacidosis | 2024 ADA consensus on high-blood-sugar crises | A fixed drip of 0.1 units/kg an hour — about 7–9 units an hour at 70–90 kg — cut to 0.05 units/kg once sugar falls below 250 mg/dL | Inseparable from what runs beside it: fluids, potassium and hourly sugar and ketone checks. Alone it drives potassium and blood sugar dangerously low. |
| Subcutaneous — self-use for muscle gain | Circulating practice in bodybuilding, outside any trial | About 10 units of fast-acting insulin after training, with carbohydrate — what case reports describe; no dose study exists | Circulating practice, not a finding: no muscle dose was ever set in someone without diabetes. The record is coma and death, and low sugar comes unannounced. |
Section 05
Protocols
No protocols featuring this peptide yet. Browse All Protocols
Section 06
Stability & Storage
Storing the product
Insulin is kept at 2–8 °C before opening, protected from freezing. Modern analogues have improved stability profiles, but as a relatively fragile protein insulin still calls for careful handling and protection from extreme heat.
After opening
In-use pens or vials can be kept at room temperature, up to 30 °C, for 28–42 days depending on the formulation. Agitation and extreme heat degrade the protein, so pens are stored away from direct heat and handled gently.
Section 07
Side Effects & Precautions
Reported effects of insulin range from the risk of low blood sugar (hypoglycemia) to local injection-site changes and rare systemic reactions.
Low blood sugar, the most significant risk
Hypoglycemia (low blood sugar) is the most significant risk. Severe hypoglycemia can cause seizures, loss of consciousness, and death.
Weight gain
Weight gain (2-4 kg) is common with insulin initiation.
Injection site lipohypertrophy
Repeated injection into the same site can cause lipohypertrophy — thickened, lumpy fatty tissue under the skin.
Metabolic and fluid effects
- Hypokalemia (low blood potassium) from an insulin-mediated shift of potassium.
- Insulin edema (fluid retention) during initial treatment.
- Peripheral edema (swelling in the limbs).
- Rare allergic reactions have been reported.
Section 08
Regulatory Status
What trips people up is not approval but jurisdiction-specific detail: a slice of the US market is sold without a prescription, and elite athletes need a documented diagnosis to use any of it legally.
FDA / United States
Approved for decades, across many formulations
Rapid-acting (lispro, aspart, glulisine), regular, NPH, long- and ultra-long-acting (glargine, detemir, degludec) and premixed insulins are all approved, plus interchangeable biosimilars Semglee (2021) and Rezvoglar (2022).
US OTC exception
Older human insulins are sold without a prescription
Regular and NPH human insulin can be bought over the counter under the 1951 Durham-Humphrey Amendment — Walmart's ReliOn brand costs about $25 a vial. Every modern analogue remains prescription-only.
WHO Essential Medicines
Listed as an essential medicine worldwide
Insulin, including long-acting analogues, sits on the WHO Model List of Essential Medicines, and WHO recommends that quality-assured biosimilar insulins be treated as interchangeable for national procurement.
EMA / Europe
Approved, with a fast-growing biosimilar wave
The EMA has cleared insulin glargine biosimilar Ondibta (positive opinion, November 2025) and insulin lispro/aspart biosimilars Bysumlog and Dazparda (February 2026), extending competition into long-acting analogues.
WADA
Prohibited under S4.4.2, not S2
WADA classifies insulins and insulin-mimetics as metabolic modulators, a non-specified substance banned at all times. Athletes with a documented diabetes diagnosis can apply for a therapeutic use exemption.
Regulatory status and prescription rules differ by country and change over time. The US over-the-counter exception for older human insulin does not exist elsewhere — check the current rules of your own regulator before relying on this.
Section 09
Research Studies
- [1]Mechanisms of Insulin Action and Insulin ResistancePetersen MC, Shulman GI. · Physiological Reviews · 2018
- [2]Biochemical and cellular properties of insulin receptor signallingHaeusler RA, McGraw TE, Accili D. · Nature Reviews Molecular Cell Biology · 2018
- [3]Insulin Receptor Signaling in Normal and Insulin-Resistant StatesBoucher J, Kleinridders A, Kahn CR. · Cold Spring Harbor Perspectives in Biology · 2014
- [4]Thirty sweet years of GLUT4Klip A, McGraw TE, James DE. · Journal of Biological Chemistry · 2019
Section 10
Frequently Asked Questions
Insulin binds its own receptor, a tyrosine kinase embedded in the cell membrane, triggering autophosphorylation and a signalling cascade through IRS proteins and PI3K to AKT. One branch of that cascade moves the GLUT4 glucose transporter from internal storage vesicles to the cell surface, allowing glucose to enter muscle and fat cells; another branch switches off glucose production in the liver by excluding the transcription factor FOXO1 from the nucleus within about 30 seconds. Together these actions pull glucose out of the blood and into storage.
In type 1 diabetes, background plus meal insulin is set around 0.4 to 1.0 units per kilogram a day, typically about 0.5 in a stable adult; this is only a starting estimate that a clinician resets within days against measured blood sugar, not a fixed program. In type 2 diabetes, background insulin usually starts around 10 units a day, or 0.1 to 0.2 units per kilogram, and is raised gradually against fasting glucose — starting doses are deliberately too low to work on their own. In both cases the number belongs to ongoing clinical monitoring, not a one-time calculation.
Using insulin without diagnosed diabetes, for example post-workout for muscle gain, has never been the subject of a dose-finding study — the roughly 10-unit amounts described in bodybuilding case reports were never established through any trial. Because insulin's central risk is hypoglycemia, and a healthy person's own pancreas already regulates blood sugar without it, exogenous insulin removes that natural safety margin; the documented outcomes in this off-label use include coma and death.
Weight gain of about 2 to 4 kilograms is a recognised and common effect when insulin therapy is started, alongside a related risk of low potassium from insulin's effect on cellular potassium shift. Both are listed among its established side effects in people using it for diagnosed diabetes, distinct from any use outside that context, which carries its own, separately documented risks.
Not the same mechanism. Insulin itself binds a cell-surface receptor and directly triggers the machinery that moves glucose transporters and switches off liver glucose output — an action independent of the body's own insulin supply. GLP-1 receptor agonists work upstream of that, prompting the pancreas to release more of a person's own insulin; that difference in where each drug acts is why the two are sometimes combined in treatment rather than treated as interchangeable.
Unopened insulin is kept refrigerated at 2 to 8 °C and protected from freezing. Once a pen or vial is in use, most formulations can be kept at room temperature, up to 30 °C, for 28 to 42 days depending on the specific product — the exact window varies by formulation, and agitation or heat exposure degrades the protein regardless.