I suppose some people would argue that 'no known side effects' extends to 'no known effects' as well in this case. Scientific evidence that it does anything at all in humans appears to be non-existent to very weak at best.
Probably half of the world's peoples have had good effects from ginseng, whether that is "placebo" (as scientist and western doctors might say...) or based on chemical compounds that haven't been extracted yet (they are still extracting them from another plant medicine in use for over 5000 years called Cannabis...scientists have no idea about most of the 500 or so in that plant either), or based on some kind of spiritual element as is said about Ayahuasca and Peyote is really all besides the point. Ginseng has cured many people and kept many more from ever getting ill in the first place.
Explain it however you want.
But I must stress this: if you have cancer, don't eat herbs and pray, go to a damn doctor.