Side effects of coenzyme Q10 include upset stomach, nausea, loss of appetite and diarrhea, according to WebMD. Most people do not experience severe side effects when taking coenzyme Q10, and side effects are minimized if the daily dose is taken in small amounts throughout the day.
Healthy people should take no more than 3,000 milligrams of coenzyme Q10 daily for up to eight months to avoid side effects, explains Mayo Clinic. High doses of the coenzyme may affect the levels of liver enzymes, and the medication reduces the effectiveness of warfarin medication. Coenzyme Q10 increases the risk of bleeding, which is dangerous in people who have bleeding disorders. Coenzyme Q10 sometimes causes skin itching, headache, back pain, gas and muscle pain.
Coenzyme Q10 also causes allergic reactions in some individuals, notes WebMD. The medication is shown to lower blood pressure in some as well, so people with low blood pressure should monitor their levels when taking it. People who have an upcoming surgery should stop taking coenzyme Q10 because it interferes with blood pressure control. The coenzyme should not be given to children without supervision from a doctor, as it is not known what side effects they make experience. It is also not known what side effects breast-feeding women may experience while taking coenzyme Q10.