Hibiscus tea, which has a tart flavor, has shown benefits in humans. In a study published in the Journal of Nutrition, McKay and her colleagues looked at whether the amount of hibiscus in Red Zinger (from Celestial Seasonings) could lower blood pressure in people at risk of hypertension and found that drinking three cups a day did significantly lower blood pressure after six weeks.
"It won't hurt you, but it won't help you much either," Jennings says. She notes that dandelions are rich in antioxidants and high in calcium and iron but that the amounts in tea are not enough to be beneficial. "Adding whole dandelions to a salad is the best way to get the good health effects," she says.
Peppermint tea is frequently used to aid digestion, but McKay says there are few, if any, studies of peppermint tea in human subjects. But some people should stay away from mint tea: "Mint teas are bad for people who have gastroesophageal reflux disease," because it could worsen their symptoms, she says.
Researchers at the University of Maryland note that "ginger has been used to help digestion and treat stomach upset, diarrhea and nausea for more than 2,000 years." Research studies have found that ginger can prevent motion sickness and reduce morning sickness and that it is well tolerated when used in typical doses. At high doses, ginger may cause abdominal discomfort, heartburn and diarrhea.