you decide, since its a magical house, and you are sure you can back to normal, why not go for the gold, so to speak. You uncork the bottle and swig done enoguh of the potion, which tastes like rasberry syrup, to constitue a gulp, and wait.
and wait
and wait.
Nothing's happening. It seems like it really was nothing more than a prank drink. Sadly, your dreams of finding a place where you could alter your physical being seem to be dashed.
However the drink does taste pretty good, so you store the rest of the bottle in your pocket for later, and leave the potion room. More wandering could do you good.
you wander down the halls and find a nice library, large and spacious. you step inside when you feel a burp. it comes out, and it tasters like rasberry syrup, as would be expected, but then you burp gain. then you fart, rather loudly, and your flatulance seems to have no end. the burps and the farts continue for about a minute, and when they are gone for only a moment...your entire body lurches. a tingle spreads across your skin, and your bones feel odd. the lurches continue, giving you only one clue. you are getting smaller.
no. not smaller.
younger.
your body aches and moans as your bone structure shrinks. your body hair shrinking back into your chest, as you speed backwards thru puberty. you are now an early teen, no pre-teen, and getting smaller. you were eighteen, and you drank a gulp, which takes away ten years according to the bottle, so you will be eight., "this feels wonderful!" you state as the changes slow, leaving your clothing dangling, your skin smooth, and your height almost half as high as it used to be. "eight again" you say, noticing your younger voice. "this is interesting..."