Insulin

Insulin is a peptide. That word, peptide, covers both the medicine millions of people with diabetes inject every day and the experimental molecules elsewhere in this encyclopedia. A peptide is just a short chain of amino acids: insulin is 51 of them, semaglutide is 31, BPC-157 is 15. They are the same molecular class. That doesn't make a research peptide as safe or as proven as insulin, most aren't, but it does mean that 'peptide' is a chemistry word, not an alternative-medicine category. Insulin is the proof.

The evidence base for insulin is essentially the foundation of modern diabetes care. Within months of its 1921 purification in Toronto, insulin transformed type 1 diabetes from a uniformly fatal condition into a manageable chronic disease, the 1923 Nobel Prize in Physiology or Medicine recognised exactly that. The Diabetes Control and Complications Trial (DCCT, 1993, NEJM) randomised 1,441 people with type 1 diabetes to intensive insulin therapy versus conventional care and showed a 35–76% relative reduction in the progression of retinopathy, nephropathy and neuropathy over a mean 6.5 years. The UK Prospective Diabetes Study (UKPDS 33, 1998, Lancet) in 3,867 people with newly diagnosed type 2 diabetes demonstrated that intensive glycaemic control (with insulin or sulphonylurea) reduced microvascular complications by ~25%. Long-term follow-up of both cohorts showed a 'legacy effect', early intensive control kept producing benefit decades later. The honest caveats: insulin therapy itself carries real harm. Severe hypoglycaemia is the leading cause of medication-related emergency-department visits in older adults. Analogue insulins reduce nocturnal hypoglycaemia versus older NPH and produce flatter pharmacokinetic profiles, but at substantially higher list prices; the cost-benefit case for analogues over human insulin remains contested in low- and middle-income settings. The WHO has prequalified biosimilar human insulin to address that.

For information only, insulin dosing must be set and titrated by a clinician, never from a webpage. Unlike most peptides on this site, an incorrect insulin dose is not a tolerability issue: severe hypoglycaemia from over-dosing causes seizures, coma, permanent brain injury and death. Most modern type 1 diabetes care uses a basal-bolus regimen: a long-acting (glargine, detemir, degludec) once or twice daily to cover background insulin needs, plus a rapid-acting (lispro, aspart, glulisine, Fiasp, Lyumjev) before meals dosed against carbohydrate intake and current blood glucose. Many people on intensive therapy now use continuous subcutaneous insulin infusion (a pump) paired with a continuous glucose monitor and increasingly with hybrid closed-loop algorithms. Insulin needs change with illness, exercise, menstruation, pregnancy and many other variables, which is why ongoing clinical supervision matters. Structured education programmes (DAFNE in the UK for T1D, DESMOND for T2D, equivalent programmes elsewhere) teach safe self-management and are the appropriate place to learn about dosing.

Hypoglycaemia is the headline risk. Mild lows present as shakiness, sweating, hunger and cognitive blunting; severe lows cause seizures, loss of consciousness, permanent neurological injury and death. The rescue treatments are fast-acting carbohydrate (juice, glucose tablets) for mild lows and [intramuscular](/glossary "Intramuscular: Injected into muscle tissue; typically a deeper, larger volume than a subcutaneous injection.") or intranasal glucagon for severe lows when the person can't swallow safely. Other recognised effects: weight gain (typically 2–4 kg with intensification), injection-site lipohypertrophy or lipoatrophy (rotating sites helps), rare hypokalaemia (especially during rapid hyperglycaemia correction in DKA), occasional insulin-induced oedema, and very rare allergic reactions to formulation excipients. Misuse by non-diabetic athletes is one of the most genuinely dangerous forms of peptide misuse documented. Insulin has anabolic effects on muscle (which is why it is misused in bodybuilding, often stacked with growth hormone), but a non-diabetic person who injects insulin can crash into severe hypoglycaemia hours after the dose, far enough after injection that they may be alone or asleep. Cases of permanent brain injury and death from bodybuilding insulin misuse are well documented in the literature. This is also why WADA prohibits it under section S4.5 for athletes without a diabetes diagnosis (see legal section).