Coenzyme Q10, or CoQ10, is a health supplement taken for its antioxidant and energy-boosting properties. As with many supplements, using CoQ10 comes with a risk of negative side effects. The bulk of these side effects occur when users take CoQ10 in excessive amounts.
CoQ10 is safe for adults at a daily intake level of 3000 mg, according to Mayo Clinic. Excessive doses are known to cause skin itching, gastronomic distress and headaches, but doses in the normal range may also aggravate existing instances of these conditions.
Mayo Clinic also recommends caution when using CoQ10 while taking other medicines, and it advises patients to consult a doctor because there are many medications with potential complications caused by interactions with CoQ10. This is especially important for those taking warfarin, blood pressure medications or supplements, thyroid agents and heart-regulating medications. Diabetics need to exercise caution with CoQ10 because it affects blood sugar levels. Dosage adjustments in any of these cases may allow continued intake of CoQ10.
Since bile duct blockage and liver problems both cause increased levels of CoQ10 in the body, Mayo Clinic suggests reduced doses of CoQ10 if these conditions are already present. Individuals with mitochondrial disorders risk limited mobility if taking CoQ10 as a supplement.