You know the story about the princess who has to kiss the frog to turn him back into a prince, so she can marry him and they can live happily ever after?
That fairy tale might have slightly less innocent origins: a certain kind of toad produces venom with bufotenine, a supposed ancient aphrodisiac that increased levels of serotonin, the happiness hormone, in couples looking to increase sexual arousal and get it on.
"Anything that uses serotonin increases arousal at the brain level to promote sexual activity," said Dr. Paola Sandroni, a neurologist who became fascinated with ancient aphrodisiacs when the erection-producing drug Viagra first appeared on the market. She published a scientific paper about aphrodisiacs in 2001.
Sandroni came across well-known aphrodisiacs in her research, like dark chocolate, and some more outlandish ones, like a certain kind of whale poop. A substance called ambrien, which came from the guts of sperm whales, was used in Arab folk medicine to treat headaches and improve sexual function. She found studies that showed ambrien increased certain pituitary hormones and testosterone levels to stimulate the brain's synthesis of dopamine, the pleasure chemical.
Of the more traditional aphrodisiacs, Sandroni said artichokes, oysters and avocados are debatable. It's possible they stimulate arousal, but it's also possible their reputations grew because merchants found it was good for business to claim they had aphrodisiac qualities.
"Basically, we're on really shaky ground here," said Pepper Schwartz, a professor of sociology at the University of Washington. She's written and co-written several books on sex and relationships, including her latest, "The Normal Bar."
She said the appeal of scents like rose, pumpkin and cinnamon are repeated often enough that they may have some effect in the bedroom, but the power of pheromones and aphrodisiacs lack the scientific proof to make a believer out of her.
"We may give off a smell, but not like when a female wolf is in heat and any male wolf in the next several miles can tell she's ready," she said. "The same kind of iffiness is true of true aphrodisiacs."
Schwartz said her aphrodisiac of choice is champagne, because the bubbles promote faster alcohol absorption into the bloodstream, allowing one to relax quickly. Alcohol allows people to feel free to have sex by alleviating stress and inhibitions, but Schwartz maintains it doesn't push people to have sex with partners they would not be attracted to when they were sober.
But Schwartz said she is always careful not to drink too much -- or eat too much on a fancy date.
"The two biggest physical enemies of sex are being tired and being full," she said.
Even though oysters are often considered aphrodisiacs because they have zinc, which stimulates blood flow, Schwartz said someone would have to eat a beach full of them to make a dent in their sexual arousal. That obviously puts those people in the too-full zone, she said.
The same principle is true of ginseng and dark chocolate, which are rich in antioxidants and therefore work somewhat like Viagra to increase blood flow, Sandroni said. However, it would take huge amounts of them to produce the same effect as Viagra.
Still, it's possible that regular amounts of chocolate and oysters get people in the mood simply because they're expensive and associated with fancy dates, Sandroni said. That alone could heighten serotonin and dopamine in the brain to make someone feel sexy.
"Even if an aphrodisiac isn't working on a physical level, and it's only working in a placebo-effect kind of way, there's validity to its use," said Sarah Thorp, a curator at the Museum of Sex in New York City.
Thorp, who has a background in anthropology, said Cleopatra appears in many myths about sex and pleasure. She notably used to bathe in water filled with saffron to increase sensitivity and lead to greater pleasure.
Chocolate made its way into aphrodisiac lore, Thorp said, when the Aztec emperor Montezuma drank a chocolate beverage before satisfying his numerous wives.
"Everyone's always looking for something to enliven their sexual relationships and sexual prowess," she said. "Across the world in every culture in every time period we keep on circling back to this idea of aphrodisiacs. I think that in and of itself is fascinating."