You take out the stopper, pause for a moment, and drink the first half of the five-minute penis potion, then pass the vial through the vapor-thick air to the woman. She smiles and drinks the second half without hesitation, then she stands up and stretches. "This is going to be fun." She looks down at herself, between her legs. You watch, too, but see very little. Maybe her pussy stretches a little, maybe it's just the haze in the room.
But the change that suddenly seizes your body is far less subtle. You gasp and your eyes widen as your crotch begins to burn. The woman's hungry eyes move from her own area to yours. You follow her gaze to stare down at your penis. All the talk of potions had rendered you flaccid, but the sensation and the attention causes him to peek upward. You see each heartbeat make him pulse, and each pulse bring more erect. And each pulse brings him a tiny bit larger.
You sit down, your breath caught in your throat. The woman stands over you, staring at your penis as it grows, as if it is expanding for her pleasure. You watch it as it lengthens two inches, then three. You watch its girth expand, too, becoming a thicker cylinder than you had ever seen in your life. The expansion runs from the tip of the head all the way down to where it protrudes from your body. It becomes so thick that your penis takes all the space in your pubis region, swelling so that in your sitting position, its root spreads from one thigh to the other. And it's still growing. You issue a small noise, a kind of panic slipping out as your own penis seems to become something that does not belong to you.
You stand up, becoming light-headed for just a moment, and then grab your penis and push it against your body. It has grown well past your navel and does not show signs of stopping. Each pulse pushes it longer and thicker. The whole shaft seems to ignite with intense sensation, as if the act of expanding were pleasurable. Your breathing catches in your throat for a few seconds, forcing you to breath heavily for a few seconds afterward. You feel like you've just run a race, instead of simply drank a potion. Soon, your penis feels heavy. Its base hangs off the bottom of your torso, pushing out against your inner thighs. Its head points out and away from you, except when you bring it in against your body to measure it.
After a few more minutes of this, your penis stops growing, and you are left with a massive, heavy object that reaches to the bottom of your sternum and is as thick around as your fist.
"If you're worried," said the woman, "Look at me." She sits down and spreads her legs, revealing an enlarged vaginal opening that appears exactly big enough for you to fit inside. You feel terrified of what will happen if you walk to her. She can't possibly have an opening deep enough for as much as you have grown. She welcomes you, but you hesitate.