Reported side effects from taking coenzyme Q10 include loss of appetite, nausea, stomach upset, diarrhea, vomiting, skin rashes and low blood pressure, as reported by the National Institutes of Health. Taking two half-doses during the day instead of a full dose may limit side effects.
The National Institutes of Health recommends avoiding coenzyme Q10 while breastfeeding or undergoing chemotherapy. The drug's effectiveness may be reduced by smoking, consuming omega-3 fatty acids or taking blood clotting medications, blood pressure medications or red yeast. Taking coenzyme Q10 with acacia gum may increase both its benefits and side effects. The University of Maryland Medical Center warns that coenzyme Q10 may lower blood sugar.