Who Should Not Take Coenzyme Q10?
Coenzyme Q10 has a reputation as one of the gentlest supplements on the shelf, popular with runners, people on statins and anyone interested in "cellular energy". For most healthy adults that reputation is deserved. There are, however, specific groups for whom CoQ10 is either inadvisable or should only be used with medical supervision. Our editorial team sets out who they are and why.
A brief profile of CoQ10
Coenzyme Q10 (ubiquinone, and its reduced form ubiquinol) is a fat-soluble compound present in nearly every cell. It carries electrons in the mitochondrial chain that produces ATP and acts as an antioxidant within cell membranes. The body makes its own CoQ10, and small amounts come from meat, oily fish and nuts.
Supplements typically provide 30–200 mg per day, and clinical studies have used up to several hundred milligrams. Because it is fat-soluble, it is better absorbed with a meal containing fat. Ubiquinol is marketed as more bioavailable, although the advantage varies between studies and individuals.
The most robust clinical evidence concerns heart failure. The Q-SYMBIO trial reported fewer major cardiovascular events in patients with chronic heart failure who received 300 mg per day alongside standard therapy. Evidence for sport performance is far weaker and inconsistent.
Safety assessments, including the review by Hathcock and Shao and the analysis by Hidaka and colleagues, concluded that CoQ10 is well tolerated, with an observed safe level of around 1200 mg per day in adults. Side effects, when they occur, are mostly mild digestive upset, nausea or insomnia when taken late in the day.
People taking warfarin and other anticoagulants
The most important interaction concerns warfarin. CoQ10 is structurally similar to vitamin K, and case reports have described reduced effectiveness of warfarin, reflected in a falling INR, after patients started CoQ10. A controlled trial by Engelsen and colleagues did not find a significant effect in stable patients, but the uncertainty is enough for clinicians to advise caution.
For someone on warfarin, an unnoticed drop in anticoagulation increases the risk of stroke or clot. If CoQ10 is started or stopped, the anticoagulant clinic should know so that INR can be checked more closely.
Direct oral anticoagulants such as apixaban and rivaroxaban are less likely to be affected in this particular way, but no supplement should be added to anticoagulant therapy without informing the prescriber or pharmacist.
The same principle applies to people taking antiplatelet medicines after a heart attack or stent. While no major interaction is established, combining several supplements with these drugs can make bleeding or clotting risk harder to predict.
Blood pressure, diabetes and surgery
A meta-analysis by Rosenfeldt and colleagues suggested CoQ10 may modestly lower blood pressure. In someone already on antihypertensive tablets, this could add to the effect and cause dizziness or light-headedness, particularly on standing.
Some studies have also reported small improvements in blood glucose control. For people with diabetes who use insulin or sulphonylureas, an additional glucose-lowering effect could theoretically increase the risk of hypoglycaemia, so closer monitoring is sensible when starting a supplement.
Because of possible effects on blood pressure and clotting, many surgeons and anaesthetists ask patients to stop non-essential supplements, including CoQ10, about two weeks before planned surgery. Always follow the instructions of your surgical team.
| Group | Concern | Advice |
|---|---|---|
| Warfarin users | Possible reduced anticoagulant effect | Only with clinic awareness and INR checks |
| On blood pressure medicines | Additive lowering of blood pressure | Discuss with GP; monitor readings |
| Diabetes on insulin or sulphonylureas | Possible additional glucose lowering | Check glucose more often |
| Cancer treatment | Theoretical interference with therapy | Only with oncologist's agreement |
| Pregnancy and breastfeeding | Insufficient safety data | Avoid unless advised by a doctor |
| Children | Not routinely needed | Only under specialist supervision |
Cancer treatment, pregnancy and athletes
Oncologists are often wary of antioxidant supplements during chemotherapy and radiotherapy, because some treatments work partly by generating oxidative stress in cancer cells. Evidence that CoQ10 interferes in practice is limited, but the precautionary principle applies: discuss any supplement with your oncology team.
In pregnancy and breastfeeding, there is simply not enough safety information to recommend routine use. Some research has examined CoQ10 in specific obstetric settings, but these are specialist decisions rather than self-care choices.
For healthy athletes, the question is less about danger and more about usefulness. High doses of antioxidants such as vitamins C and E have been shown in some studies to blunt training adaptations. Whether CoQ10 does the same is unclear, but there is no strong case for chronic high-dose use in people without a deficiency.
Statin users form a special case. Statins lower the body's CoQ10 production, and many people take CoQ10 to reduce muscle aches. Trial results are mixed; persistent muscle pain on statins should be reported to a GP rather than self-treated.
Conclusions of the editorial team
For healthy adults, CoQ10 has an excellent safety record at common doses. The real risks arise from interactions and from use in groups where data are lacking.
Those who should not take CoQ10 without medical guidance include:
- people on warfarin or other anticoagulants;
- people on blood pressure or glucose-lowering medicines;
- patients undergoing chemotherapy or radiotherapy;
- pregnant and breastfeeding women, and children;
- anyone due to have surgery in the next two weeks.
If you fall into one of these groups, a short conversation with your GP or community pharmacist is usually all it takes to decide whether CoQ10 is appropriate and how to monitor it.
You might also like to read our articles on statins and exercise, antioxidants and training adaptation, and how to read a supplement label for hidden interactions.
References
- Hidaka T, Fujii K, Funahashi I, Fukutomi N, Hosoe K. Safety assessment of coenzyme Q10 (CoQ10). Biofactors. 2008;32(1–4):199–208.
- Hathcock JN, Shao A. Risk assessment for coenzyme Q10 (Ubiquinone). Regul Toxicol Pharmacol. 2006;45(3):282–288.
- Mortensen SA, Rosenfeldt F, Kumar A, et al. The effect of coenzyme Q10 on morbidity and mortality in chronic heart failure: results from Q-SYMBIO: a randomized double-blind trial. JACC Heart Fail. 2014;2(6):641–649.
- Engelsen J, Nielsen JD, Winther K. Effect of coenzyme Q10 and Ginkgo biloba on warfarin dosage in stable, long-term warfarin treated outpatients: a randomised, double blind, placebo-crossover trial. Thromb Haemost. 2002;87(6):1075–1076.
- Rosenfeldt FL, Haas SJ, Krum H, et al. Coenzyme Q10 in the treatment of hypertension: a meta-analysis of the clinical trials. J Hum Hypertens. 2007;21(4):297–306.
