I've been reading about curcumin and it seems to have been pretty useful in numerous clinical trials (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3535097/), although its biodisponibility is "abysmal" (less than 1% https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5346970/). This seemed contradicting so I did a quick research and it turns out it is considered a PAIN and an IMP. However, I can't fully understand what both of those things are. Do they imply each other? How is a compound proven to be a PAIN or an IMP? Can a PAIN or an IMP have a good clinical value? Is there a mechanism in which curcumin, in spite of having such a low biodisponibility, could have such a great effect overall in health? Thanks in advance.