Common side effects of using coenzyme Q-10 include nausea, vomiting, diarrhea, appetite loss and upset stomach, according to WebMD. Some patients experience reduced blood pressure and allergic skin rashes. To minimize side effects, patients should take the total dose in reduced portions throughout the day, rather than all at once.
Most adult patients tolerate coenzyme Q-10 well, notes WebMD. Chemotherapy patients should exercise caution when taking coenzyme Q-10, as it can decrease the effectiveness of certain medications. Women can safely take Q-10 during the second half of pregnancies, but the effect of the supplement on breast-feeding mothers is not known. While the supplement is probably safe for children, caregivers should not administer the substance to children unless advised by a doctor.