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This book featured something called "The Labyrinth" that was a kind of maze that opened into other worlds.
There was one world where all the men were stupid and used as sex objects.
There was a drug that had to be taken regularly by pressing/popping a bead of it onto your skin, and it got into one woman's brain and corrected her eyesight.
I read this book in about 2005.
Does anyone recognise this book?