I have gone to many many many drug rep dinners (over 20) on PREP and other HIV medications. I am a RN and have also worked in infectious disease... I'm sorry, but I haven't not heard of that once mentioned. With other medications and vitamins, yes, it's true. I would caution making a blanket statement like that from some guy on youtube. I have taken fiber every day for years and I eventually got on PREP after going to many presentations on the research behind it. It definitely would have rang some alarms in my head about he fiber and Prep interaction. My Roomate is a HIV doctor and knows I take prep and fiber and has never said a word to me about it either. There definitely isn't any harm in taking the two medications several hours apart though.