There is nothing about herbs that automatically makes them non-toxic just because they are natural.
Medicinal herbs contain powerful, pharmacologically active compounds.
In other words, they contain drugs, and like any drugs, they should be approached with caution. This means, for example, that pregnant women should be as careful about medicinal herbs herb-based treatments as they are about conventional medicines. Some compounds in herbs can cross the placenta and are clearly linked to birth defects or other problems in newborns. People on certain medications, like heart or blood pressure medications, anti-coagulants and psychiatric drugs, can have serious problems from interactions between the herb and the medicine they're taking. Many physicians are not well informed about herbs, and so you cannot always rely on your doctor to know about potential problems.