Question: Are most herbs and vitamins basically safe?
Answer: No, the myth that if it's natural it's safe is the myth that is the most dangerous for people. Patients will say they take a particular herb because they know someone who took it and felt better or they know someone who knows someone who took it and felt better. Herbs are medicine, and they should be taken as medicine -- with the same respect that we give to prescription medicines.
Just because it's an unstandardized or nonstandardized industry in the United States doesn't mean that it's just safe to take any amount. Herbs can interfere with sleep; herbs can cause you to feel sleepy or have a sedative effect -- as a side effect; you may be taking it for a different reason. Herbs can alter your blood clotting mechanism, which is of course a concern with patients who are on cancer therapy.
So, if it's natural it's not necessarily safe and it should be listed and treated as a medication. If you're taking an herb because you have allergies or you have a cold, it doesn't mean it can't interfere with your cancer therapy. So, herbs are not like "smart bombs." They don't only affect one organ system, they affect your whole body, and therefore can interact with the drugs that you're taking.
And you should never, never take an herb for the same reason you're taking a prescription medication, because it will definitely lead you to the potential for a drug reaction, herb-drug reaction.