For centuries, people from various cultures have used certain plants for sexual enhancement, from boosting libido to improving erectile function to increasing lubrication in women. According to medicine hunter Chris Kilham, the power of many of these natural, plant-derived aphrodisiacs has been verified by clinical studies—and modern science has only begun to scratch the surface. Chris has traveled the world investigating medicinal plants and teaches ethnobotany at the University of Massachusetts at Amherst. He has authored 13 books, including Hot Plants: Nature's Proven Sex Boosters for Men and Women, which focuses on sex-enhancing plants. Chris shares just a few natural agents of desire with Dr. Oz:

Rhodiola rosea is a plant native to Siberia that radically reduces cortisol levels in the blood, thereby reducing stress and enhancing sexual function, Chris says. According to Chris, dosages between 100 and 300 milligrams a day have been proven effective in human studies. Moreover, Chris says rhodiola rosea enhances brain function, mood, cardiovascular function and immune function, and boosts energy, stamina and endurance. "When you take it, you feel it, and you feel good," says Chris, who takes it every day. "I feel more energetic, more lively, more clear minded."

Maca is a root resembling a turnip that is a staple food in the Peruvian highlands. Chris says maca contains compounds that significantly boost sexual desire, alleviates erectile dysfunction and also helps women relieve the uncomfortable symptoms of menopause, especially hot flashes and night sweats. There are products containing maca extract as well as maca powder that can be added to shakes or used like flour in cooking, Chris says.

Tongkat ali is a tree root from Malaysia that has been used in Southeast Asia for hundreds of years for the treatment of malaria as well as improving various sexual parameters, Chris says. According to Chris, tongkat ali has been shown to help alleviate erectile dysfunction, boost testosterone levels in males and progesterone levels in females, and may have cancer-inhibiting properties. He says it's a safe and effective substitute for brand-name drugs used to treat erectile dysfunction.