From the name, I was guessing it's a brand or manufactured version of vasopressin, also called anti-diuretic hormone.
Your hypothalamus is the organ which monitors your hydration level. As your hydration level drops to or below the ideal levels, the hypothalamus starts generating vasopressin. Kidneys naturally lose a lot of water from your body as part of their filtration process, but they have a post filtration phase, which in the presence of vasopressin, recovers the water from your urine and feeds it back into your blood supply. This is also a key mechanism for maintaining your blood pressure. Your bladder also has a limited ability to recover water from urine if you become dehydrated after the urine has already passed into the bladder. (This can happen if you suddenly start doing something that makes you sweat such as exercise, and some people occasionally notice this might remove an earlier sense that you needed to have a pee.)
The organ in your body which knows if it's day or night is the pituitary gland. During the day, this steals and stores some vasopressin. During the night, given you aren't expected to be drinking or increasing your hydration level, it releases the stored vasopressin to recover water from urine, but in this case it's to reduce the volume of urine collected, so you can go all night without needing to wake to pee (if everything is working correctly). In the morning, you usually have a pee to get rid of what was collected overnight (and if you're asked to collect a urine sample, it's this overnight collection which is preferred). Many men find that shortly afterwards, they need a pee again, and that's because the pituitary will have stopped releasing stored vasopressin, so your kidneys start pumping out the excess water that was returned to your blood overnight. This is also why blood pressure often goes up at night (effectively, blood pressure regulation is disabled to prevent your bladder filling too much), and more strokes happen at night. It's also why it's a bad idea to drink much before you go to bed or during the night.
The whole process of vasopressin and day/night changes tends to become less effective with age, and that's one reason which can contribute to needing to pee more at night as we age (although probably not the main reason). Vasopressin is available as a drug to take at night to help counter this reduction in efficiency, but as it also effectively disables blood pressure regulation overnight, it comes with a load of safety caveats, such as not drinking overnight or even taking the pill with water, and it's not much used. However, it might help some men in some circumstances.