My impression is that lumped as a (extremely broad and diverse) whole that OTC supplements, when studied rigorously in humans in vivo, have generally not been f

My impression is that lumped as a (extremely broad and diverse) whole that OTC supplements, when studied rigorously in humans in vivo, have generally not been found to be terribly effective for most maladies. Many have been often found to have poor quality control, often adulterated with other substances, provided in poorly bioavailable forms, or sometimes not actually containing the substance they claim to contain. As a whole they generally get a bad rap in medical school and among physicians. So I wonder if this study reflects a tendency of some patients to disregard or be less adherent to the treatment plan recommended by their oncologists, who seem unlikely to recommend dietary supplements that lack large supporting RTCs. Or perhaps, as mentioned, if they didn't properly control for severity of disease, it is not uncommon for a provider to give a "sure, why not" when a patient with severe / terminal disease is interested in an unconventional but low cost and likely low harm intervention.