Written by Mario Rottorf, Helen Cooke and the CAM-Cancer Consortium.
Updated June 21, 2016

Coenzyme Q10

Is it safe?

Two reviews of preclinical and clinical data concluded that CoQ10 is very safe as a dietary supplement 33;34. The observed safety level (OSL) is 1200 mg/day, and oral administration for up to 30 months is regarded as safe 33. In children, a daily dose of max. 10mg/kg body weight is considered safe; in pregnant women, a maximum of 200mg/day 35

Adverse effects

The dose-dependent adverse effects that have been documented are nausea, acid reflux, upper abdominal pain, allergic dermal reactions, sensitivity to light, dizziness, irritability, headache, fatigue, and, if taken in the evening, mild insomnia. The prevalence of adverse events is reported at < 1% of users 8;37;38. Doses over 100mg/d should be redistributed to 2-3 doses per day 38. A monograph issued by the Natural Medicines Comprehensive Database (NMCD) reports several different clinical studies in which no severe adverse events occurred 35


There are no mentions of any contraindications for CoQ10 supplements in international literature 35

Drug interactions

Theoretically, CoQ10’s antioxidant mechanism of action could mean that it may impact the efficacy of some chemotherapeutic agents (such as anthracycline and cyclophosphamide) as well as radiotherapy. Recent in-vitro studies, however, have shown that CoQ10 does not affect the antineoplastic properties of doxorubicin 39.

There are individual case reports which suggest that CoQ10 can reduce the efficacy of coumarins 40-42, a phenomenon that can be explained by the structural similarity between CoQ10 and Vitamin K 2. A small-scale randomised trial showed no change in the INR levels of patients who received coumarins and CoQ10 in doses of up to 100mg/d for four weeks 43.

Taking CoQ10 can lower the need for insulin in patients with diabetes 8;44 and the Natural Medicines Comprehensive Database describes CoQ10’s potential hypotensive effects which should be taken into account in antihypertensive treatment 35.

Quality issues

The quality and composition of CoQ10 products may differ between manufacturers 45;46.


Mario Rottorf, Helen Cooke, CAM-Cancer Consortium. Coenzyme Q10 [online document]. http://www.cam-cancer.org/The-Summaries/Dietary-approaches/Coenzyme-Q10. June 21, 2016.

Document history

Revised in September 2016 by Mario Rottorf and Helen Cooke
Assessed as up to date in April 2014 by Barbara Wider.
Revised and updated in December 2012 by Helen Cooke.
Fully revised and updated in September 2011 by Helen Cooke.
Fully revised and updated in August 2009 by Helen Cooke.
First published in 2005, authored by Helen Seers and Helen Cooke.


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