CoQ10 is sold in the United States as a nutritional supplement. Thus, there are no established dosage guidelines. Adults typically use a CoQ10 supplement that provides between 30-100 mg per day, although people with specific health conditions may supplement with higher levels (with the involvement of a physician). Most of the research clinical studies conducted on heart conditions have used 60-150 mg of CoQ10 per day.

Studies indicate that preventive dosage for patients with cardiovascular concerns or those taking one of the statin drugs to lower cholesterol, is between 30 mg and 150 mg/day, while cancer patients or patients with compromised immune function may require higher dosage.

A clinical study published in 1994 shows a dose dependent relationship in the effects of CoQ10 treatment for women with high-risk breast cancer. In one patient, during therapy for about one year with 90 mg. of CoQ10 daily, the tumor "stabilized". When the dose was increased to 390 mg. daily, after one month the tumor was no longer palpable. After another month, mammography confirmed the tumor was no longer present (Lockwood, K., Moesgaard, S., Flokers, K., "Partial and Complete Regression of Breast Cancer in Patients in Relation to Dosage of CoEnzyme Q10" Biochemical and Biophysical Research Communications, Vol. 199, No. 3:1504-1508, 1994.)

People with cancer who consider taking much higher amounts should discuss this issue with a doctor before supplementing. There are several anecdotal reports of large amounts of CoQ10 resulting in improvements in certain types of cancer. However, controlled trials are needed to confirm these preliminary observations.

Most doctors recommend that CoQ10 be taken with meals to improve absorption. Generally it takes one to three months to experience benefits from supplementation, and as long as six months for maximal effects to occur.