There have been no reports of significant adverse side effects of oral coenzyme Q10 supplementation at doses as high as 2,400 mg for 8 weeks (64), 1,200 mg/day for up to 16 months (39) and 600 mg/day for up to 30 months (45).
Some people have experienced gastrointestinal symptoms (e.g., nausea, diarrhea, appetite suppression, and heartburn), which may be minimized if daily doses higher than 100 mg are divided into two or three daily doses. However, the lack of a dose-response relationship between Coenzyme Q10 and the symptoms suggest that the effects are not related to the coenzyme Q10 content in the capsules. Thus, in human studies no adverse effect causally related to coenzyme Q10 has been identified.
Because controlled safety studies in pregnant and breast-feeding women are not available, the use of coenzyme Q10 supplements by pregnant or lactating women should be avoided (63).
Presently, no tolerable upper intake level (UL) has been set for coenzyme Q10.
Because of the potential for interactions, dietary supplements should not be taken with medication without first talking to an experienced healthcare provider.
Authored by Dr Peter Engel in 2010, reviewed and revised by Dr. D. Raederstorff on 12.04.2017