Oxytocin vs Vasopressin: what is the difference?

How they differ

These two are so similar that they are almost the same molecule: nine amino acids each, differing at only two positions, and both released from the posterior pituitary. That near-identity means each has some activity at the other's receptors, which is one reason their effects are hard to separate cleanly in studies. Oxytocin drives uterine contraction and milk letdown and is the one that gets written about for social bonding. Vasopressin, also called antidiuretic hormone, tells the kidney to reclaim water and constricts blood vessels, so it is the one that governs how concentrated your urine is. Both are peptides, so neither is absorbed usefully from the gut.

Side by side

Structural similarity 0.71 of 1, computed as a Morgan fingerprint Tanimoto coefficient. It measures shape, not effect.

Common questions

What is the difference between Oxytocin and Vasopressin?

These two are so similar that they are almost the same molecule: nine amino acids each, differing at only two positions, and both released from the posterior pituitary. That near-identity means each has some activity at the other's receptors, which is one reason their effects are hard to separate cleanly in studies. Oxytocin drives uterine contraction and milk letdown and is the one that gets written about for social bonding.

Is Oxytocin bigger than Vasopressin?

Vasopressin is the heavier molecule, 1,084.2 g/mol against 1,007.2 g/mol for Oxytocin. Oxytocin is C43H66N12O12S2 and Vasopressin is C46H65N15O12S2.