One of my mates tried 300mg of Niacin on possibly half empty stomach.
as i was with him, he reported to me that it felt like his throat was getting swallon i.e it was closing, in a way it was really hard for him to breath, then straight after his stomach started hurting. all up lasting 5 minutes. all of which happened right when the flush kicked in
i was told it was something he never felt before.