The bottle contains a thin iridescent liquid, It's reflected colors appears to constantly change in an undiscernible manner, with you being unable to comprehend exactly how or why the color scheme changes, and never able to describe what colors or pattern it reflects at any given time.
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A creature who drinks the liquid in this bottle must make a DC14 CON Save.
+A creature who drinks the liquid in this bottle must make a DC14 CON Save, with the DC increasing by 2 for each bottle the creature has previously drank since their last Long Rest. The creature takes 4d8 damage on a failed save, or half on a successful save. A creature who rolls a Natural 1 on their save also falls unconscious for 1d4 hours, though can be woken up if another creature spends an action to wake them. A creature who clears the DC by at least 5 (meaning 19 or above for DC14) takes no damage. A creature who succeeds on their saving throw regains a 1st level spell-slot.