Yes, supplements don't appear on most interaction charts because it's impossible to know what's in most of them and what doses people are taking. There is no doubt that some will interact, and some won't but we don't know which ones.
On the general topic it's probably worth reading this:
The main ones I want to continue taking are Collagen, Glucosamine /chondroitin and gelatin. I really feel that these have been helpful with my arthritis. My fingers used to lock up all the time and would be stuck and I couldn't bend them. Since I have taken these, this went away. My rheumatologist felt they would also be helpful with the pain in my knees.
My gastroenterologist put me on milk thistle years ago and I wondered if I should continue this since he felt it was helpful for my liver. I wondered if this is why my biopsies were all a number 1 when they rated them and they were done at 3 years after the diagnosis and then repeated 7 years after that. All 3 biopsies were the same.
Also, I feel I should continue my vitamins because of my sleeve gastrectomy, I don't absorb everything from food and my meals are very tiny. I take b12 and D
While I suspect it should not interact, the best treatment for HCV related liver disease is to get rid of the HCV so stopping milk thistle during treatment avoids any worry of interaction. The major benefits are flowing from the DAAs. You can continue it after, but after treatment, you'll find your liver enzymes are normal and you can't get better than that - the cause is gone so...
In general, as far as your body is concerned, collagen and gelatin are just different forms of protein. They will be digested in your gut into their constituent amino acids and from there do no more, no less than eating a little chicken, red meat or fish. I'd rather have the real food myself, it's tastier and more natural.
That said, undenatured type II collagen (UC-II) is not intended to be used by your body as a collagen re-builder. In a process called oral tolerance, very small doses of UC-II are taken to train your body’s immune system to stop attacking its own collagen