Date rape drugs

After reading up on the 3 main drugs used for date raping girls I started wondering what effect does a drug has to have to be categorized as date rape. They all seem like drugs that makes woman unable to recall what happened… but how about slipping Vitara into their drink making them extremely horny and just want to do you right there?

That being said, I wonder if any girl ever slipped any viagra into guy's beer so he'd fuck her and she'd have his child so they can get married and get divorced in order for her to get half his money.