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Coenzyme Q10
What is it? Overview Usage Side Effects and Warnings

Coenzyme Q10 Side Effects and Warnings

Written by FoundHealth, ColleenO.

Safety Issues

In general, CoQ 10 appears to be extremely safe. No significant side effects have been found, even in studies that lasted a year. 1 However, people with severe heart disease should not take CoQ 10 (or any other supplement) except under a doctor's supervision.

As noted above, two studies suggest that CoQ 10 might reduce blood sugar levels in people with diabetes. 2 While this could potentially be helpful for treatment of diabetes, it might present a risk as well; people with diabetes who are using CoQ 10 might inadvertently push their blood sugar levels dangerously low. However, another trial in people with diabetes found no effect on blood sugar control. 3 The bottom line: If you have diabetes, make sure to track your blood sugar closely if you start taking CoQ 10 (or, indeed, any herb or supplement).

CoQ 10 chemically resembles vitamin K . Since vitamin K counters the anticoagulant effects of warfarin (Coumadin), it has been suggested that CoQ 10 may have the same effect. 4 However, a small, double-blind study found no interaction between CoQ 10 and warfarin. 5 Nonetheless, in view of warfarin’s low margin of safety, prudence indicates physician supervision before combining CoQ 10 with warfarin.

CoQ 10 might also interact with reverse transcriptase inhibitors used for treatment of HIV (for example, lamivudine and zidovudine). These medications can cause damage to the mitochondria, the energy-producing subunits of cells, leading in turn to a variety of side effects, including lactic acidosis (a dangerous metabolic derangement), peripheral neuropathy (injury to nerves in the extremities), and lipodystrophy (cosmetically undesirable rearrangement of fat in the body). The supplement CoQ 10 has been tried for minimizing these side effects, but unexpected results occurred. In a double-blind, placebo-controlled study, use of CoQ10 improved general sense of well-being in people with HIV-infection using reverse transcriptase inhibitors; however, for reasons that are unclear, it actually worsened symptoms of peripheral neuropathy. 6 For this reason, people with HIV who have peripheral neuropathy symptoms should use CoQ 10 only with caution.

The maximum safe dosages of CoQ 10 for young children, pregnant or nursing women, or those with severe liver or kidney disease have not been determined.

Interactions You Should Know About

You may need more CoQ 10 if you are taking:

  • Cholesterol-lowering drugs in the statin family
  • Red yeast rice
  • Beta-blockers (specifically propranolol metoprolol , and alprenolol )
  • Antipsychotic drugs in the phenothiazine family
  • Tricyclic antidepressants
  • Methyldopa
  • Hydrochlorothiazide
  • Clonidine
  • Hydralazine
  • Oral diabetes drugs (especially glyburide, phenformin, and tolazamide)

You should not take CoQ 10 except on a physician's advice if you are taking:

  • Coumadin (warfarin)

CoQ 10 might improve general sense of well-being, but worsen peripheral neuropathy symptoms if you are taking:

  • Reverse-transcriptase inhibitors (for HIV infection)


  1. Lampertico M, Comis S. Italian multicenter study on the efficacy and safety of coenzyme Q 10 as adjuvant therapy in heart failure. Clin Investig. 1993;71(suppl 8):S129-S133.
  2. Singh RB, Niaz MA, Rastogi SS, et al. Effect of hydrosoluble coenzyme Q 10 on blood pressures and insulin resistance in hypertensive patients with coronary artery disease. J Human Hypertens. 1999;13:203-208.
  3. Eriksson JG, Forsen TJ, Mortensen SA, et al. The effect of coenzyme Q 10 administration on metabolic control in patients with type 2 diabetes mellitus. Biofactors. 1999;9:315-318.
  4. Spigset O. Reduced effect of warfarin caused by ubidecarenone [letter]. Lancet. 1994;344:1372-1373.
  5. Engelsen J, Nielsen JD, Winther K. Effect of coenzyme Q 10 and Ginkgo biloba on warfarin dosage in stable, long-term warfarin-treated outpatients. A randomised, double-blind, placebo-crossover trial. Thromb Haemost. 2002;87:1075-1076.
  6. Christensen ER, Stegger M, Jensen-Fangel S, et al. Mitochondrial DNA levels in fat and blood cells from patients with lipodystrophy or peripheral neuropathy and the effect of 90 days of high-dose coenzyme Q treatment: a randomized, double-blind, placebo-controlled pilot study. Clinical Infectious Diseases. 2004;39:1371-1379.


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