Side effects of CoQ10 include dizziness, fainting, diarrhea and trembling. Other side effects include fungal skin infection, back pain, sore throat and stomach pain. Some people may experience sinus inflammation, runny nose, urinary infection or constipation, according to Mayo Clinic.
Additional side effects of Co10 include changes in sperm motility, abnormal breathing, loss of appetite and heart dysfunction. Some people may feel irritable after taking CoQ10. Other side effects include insomnia, symptoms of the flu, respiratory infection and muscle pain. Some people may experience night sweats, fatigue, gas or heart attack, states Mayo Clinic.
Prolonged use of CoQ10 should be done carefully. Taking more than 300 milligrams of CoQ10 daily can affect liver enzymes. People who take medications for regulating heart rate should be cautious when using CoQ10, as it may affect their heart rates. People who take thyroid medicines or have thyroid conditions should be cautious when using CoQ10, as it may affect thyroid hormone levels, notes Mayo Clinic.
Because CoQ10 can affect blood pressure, people who take medications or supplements for blood pressure should consult a doctor before taking it. CoQ10 can affect blood sugar levels, so people with diabetes or other related conditions should use CoQ10 carefully. People with stomach problems may want to avoid CoQ10, as it can worsen symptoms, according to Mayo Clinic.