Vomiting, nausea, loss of appetite and diarrhea are potential side effects of taking a 400-milligram supplement of coenzyme Q-10, reports WebMD. Other possible side effects are an allergic skin reaction and very low blood pressure, Mayo Clinic states.
People undergoing chemotherapy are advised to use coenzyme Q-10 carefully, as it can interfere with some types of chemotherapy drugs, according to WebMD. Additionally, the use of a coenzyme Q-10 supplement should be discontinued at least two weeks prior to having surgery, because it can compromise normal blood pressure regulation before or following a surgical procedure. Coenzyme Q-10 also increases the risk of a hemorrhage and may decrease physical ability in people with mitochondrial dysfunction, reports Mayo Clinic.
Taking coenzyme Q-10 supplements can produce side effects at any dosage, although manufacturers typically recommend taking between 22 and 400 milligrams per day. Coenzyme Q-10 is generally considered safe when taken up to 3,000 milligrams per day for as long as eight months, states Mayo Clinic. However, dosages over 300 milligrams per day may affect liver enzymes and caution should be exercised when using high doses of coenzyme Q-10 for an extended time. The risk of side effects from taking coenzyme Q-10 may be reduced by separating a total daily dose of coenzyme Q-10 into smaller portions, explains WebMD.