Ginger

Ginger, peeled and cut

Ginger is not only a spice but can also be used as a tea and has apparently some medicinal purposes. Having said that, the studies about the medicinal use of ginger vary and sometimes contradict themselves.
If you keep your intake on a normal dose, you should be fine. If you would like to get a bit more information, there is an article on wikipedia about ginger which also deals with the use of ginger in folk medicine.