Antidiuretic hormones—think vasopressin (ADH) and its therapeutic “cousins”—are basically your body’s water-balance thermostat. When they’re doing their job (or when you’re taking them as medication), the message to your kidneys is simple: hold onto water when you need to, let go when you don’t. Coffee, meanwhile, lives in a totally different lane: warmth in your hands, aroma in your face, and that gentle (sometimes not-so-gentle) nudge of alertness from caffeine.