One 4-week randomized controlled trial found that American ginseng reduced the anticoagulant effect of warfarin when the two were combined.[1] However, the study included participants without clotting disorders who received warfarin for only 3 days, making it challenging to determine the relevance of this interaction for individuals who regularly take warfarin.
Another study indicated that American ginseng may increase oxidative stress in postmenopausal women when administered at low dosages (1 gram per day) over a period of 4 months.[2]