Oxytocin is a nonapeptide hormone made in the hypothalamus. The synthetic injectable form (Syntocinon in the UK, Pitocin in the US) is a long-approved hospital medicine used to induce labour, augment contractions and prevent postpartum bleeding. The popular "love hormone" framing of intranasal oxytocin for bonding, autism and anxiety is not an approved use and the trial evidence is largely disappointing.
Insulin is a peptide. It is the 51-amino-acid hormone the pancreas releases to tell cells to take sugar out of the blood, and it is the medicine people with type 1 diabetes inject every day to stay alive. Purified in Toronto in 1921, it was the first peptide therapeutic and is on the WHO List of Essential Medicines. The same word — peptide — covers both this and the rest of the molecules in this encyclopedia.
Both peptides share an evidence grade of A. The right choice depends less on the data and more on what you're trying to do — Oxytocin for induction and augmentation of labour, Insulin for type 1 diabetes (lifelong replacement).
FDA-approved (Pitocin) and EMA/MHRA-approved (Syntocinon) for medically indicated induction of labour and augmentation of inadequate uterine contractions. Used hospital-wide as a continuous IV infusion under fetal monitoring.
First-line uterotonic for active management of the third stage of labour and for treating postpartum haemorrhage. Recommended by the WHO, NICE (NG235) and most national obstetric guidelines.
Approved adjunct after caesarean section to assist uterine contraction and reduce blood loss.
The defining indication. People with T1D produce essentially no endogenous insulin and require exogenous insulin to live. Modern care uses basal-bolus dosing (long-acting once or twice daily plus rapid-acting at meals) or continuous subcutaneous insulin infusion via pump. The DCCT established that intensive insulin therapy substantially reduces long-term microvascular complications.
Recommended by NICE and ADA when HbA1c targets are not met with metformin, GLP-1 receptor agonists, SGLT2 inhibitors and other oral agents. Often started as basal insulin alongside existing therapy. UKPDS demonstrated that intensive glucose control (including with insulin) reduces microvascular complications in T2D.
First-line pharmacotherapy in pregnancy when diet, exercise and (where used) metformin do not achieve glycaemic targets. Insulin does not cross the placenta in clinically meaningful amounts and has the longest safety record of any glucose-lowering therapy in pregnancy.
In hospital, oxytocin has a well-characterised safety profile but is not a benign drug. Excess uterine stimulation can cause tachysystole, uterine rupture (especially with a scarred uterus) and fetal distress; that is why the infusion is titrated against contractions and fetal monitoring. Oxytocin has a structural similarity to vasopressin and at high cumulative doses with large free-water infusions can cause water retention and hyponatraemia, occasionally severe. Cardiovascular effects (hypotension, tachycardia) are dose-related and more pronounced with rapid IV bolus, so the medicine is given as an infusion. Anaphylaxis is rare. For the unlicensed intranasal "wellness" products, the principal safety problem is not the molecule itself — intranasal oxytocin in trials has generally been well tolerated short-term — but the supply chain: research-chemical and compounded preparations have unverified content, sterility and labelling, and they are not regulated like the hospital drug.
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).
Both peptides share an evidence grade of A. The right choice depends less on the data and more on what you're trying to do — Oxytocin for induction and augmentation of labour, Insulin for type 1 diabetes (lifelong replacement).
Pepwyse comparison pages are generated from the same structured data behind each peptide profile. Want a different head-to-head? Use the compare picker or ask Oxytocin directly via the Ask-Peppy button. Not medical advice — see how we grade evidence.