Coenzyme Q10 has been associated with documented reports of potential interactions with warfarin.

– Am J Health Syst Pharm 2000 Jul 1;57(13):1221-7; quiz 1228-30 —
Potential interactions between alternative therapies and warfarin. — Heck AM, DeWitt BA, Lukes AL.

Adverse effects with CoQ10 supplementation are rarely reported, but include headache, heartburn, fatigue, and increased involuntary movements at high doses of 600 mg to 1200 mg per day. Mild diarrhea and skin reactions have also been reported.

Adverse reactions to Co-Q10 include anorexia, diarrhea, epigastric discomfort, ischemic tissue damage – tissue damage due to a deficiency in blood in a specific part of the body (during intense exercise), and mild nausea.

– Fetrow CW, Avila JR. Professional’s handbook of complementary and alternative medicines. Springhouse, Pennsylvania: Springhouse Corporation 1999:178-80.

Results suggest that prolonged intake of CoQ(10) in low amounts has no discernable impact on cognitive and motor functions whereas intake at higher amounts exacerbates cognitive and sensory impairments encountered in old mice. These findings do not support the notion that CoQ(10) is a fitness-enhancing or an “antiaging” substance under normal physiological conditions.

– Prolonged intake of coenzyme Q10 impairs cognitive functions in mice. — Sumien N, Heinrich KR, Shetty RA, Sohal RS, Forster MJ. — J Nutr. 2009 Oct;139(10):1926-32. Epub 2009 Aug 26.