The Q-SYMBIO trial
Q-SYMBIO is the one sizeable trial behind the claim that coenzyme Q10 (CoQ10) helps people with heart failure live longer: over two years, major cardiovascular events roughly halved on 300 mg a day. But its short-term goals showed no difference, its death results were secondary, it was part-funded by CoQ10 makers, and no larger trial has confirmed it.
Q-SYMBIO is a reason for someone with heart failure with reduced ejection fraction to raise CoQ10 with their cardiologist, as an add-on to standard treatment and never instead of it. It is not strong enough to have changed guidelines, and the current US guideline does not recommend it.
What the trial tested
CoQ10 is a fat-soluble molecule the body makes itself; it carries electrons in mitochondria, the cell's power plants, and people with advanced heart disease often have low levels of it. Q-SYMBIO gave 420 patients with moderate-to-severe chronic heart failure 100 mg of CoQ10 three times a day (300 mg/day) or placebo, on top of their standard therapy.[1] Like the other trial that moved a hard endpoint, KiSel-10, it used plain ubiquinone, not the pricier ubiquinol.
What it found
- Short term: nothing. The goals at 16 weeks — symptom class, walking distance and a heart-strain blood marker — showed no difference between groups.
- Long term: fewer major events. The long-term primary endpoint, major cardiovascular events over two years, roughly halved: 15% against 26%.
- Deaths: about halved, but secondary. Cardiovascular death and death from any cause were each also about halved, but they were reported as secondary results, which a trial is not designed to prove.[2]
Why the result is weaker than it looks
It stands alone. No larger trial has since confirmed it. The 2021 Cochrane review pooled eleven trials and concluded CoQ10 "probably reduces" death from any cause and heart-failure hospitalisation — a roughly 8% absolute reduction in deaths, so about thirteen patients treated to prevent one. But its mortality estimate comes from Q-SYMBIO alone and its hospitalisation estimate from two trials (about 1,060 people). Results for heart attack and stroke were inconclusive rather than null, and the authors concluded there is no convincing evidence to support or refute CoQ10 for heart failure.[3]
A bigger meta-analysis doesn't rescue it. A 2024 pooling of 33 randomized trials found all-cause mortality about a third lower (relative risk 0.64) and heart-failure hospitalisations roughly halved (relative risk 0.50). But it combines a few larger trials with many small ones, most rated low quality (only six described how they randomised), so its apparent precision overstates the certainty.[4]
Guidelines are unmoved. The current US heart-failure guideline (2022) does not recommend nutritional supplements in heart failure with reduced ejection fraction except to correct a specific deficiency, and notes that concerns about Q-SYMBIO's slow recruitment "have tempered enthusiasm" for CoQ10 in practice.[5]
Industry funding. Q-SYMBIO was funded in part by three commercial backers: the International Coenzyme Q10 Association, Pharma Nord, and Kaneka, the world's largest ubiquinone manufacturer.[6]
Which heart failure it applies to
Most of the evidence comes from people whose heart muscle is weakened and pumps poorly (reduced ejection fraction). For the other common type, where the heart pumps normally but is stiff (preserved ejection fraction), a 2026 review found only three small, short trials (264 people, 8–24 weeks) and concluded the evidence is insufficient to say whether CoQ10 helps.[7]
What to do
- If you have heart failure with reduced ejection fraction, CoQ10 is worth discussing with your cardiologist — as an add-on, at the trial's 300 mg a day, taken with a meal containing fat.
- Never stop or swap a prescribed heart-failure drug for it. The trial tested CoQ10 on top of standard therapy.
- If you take warfarin, tell the prescriber before starting or stopping CoQ10 and have your blood clotting test rechecked. The details are on Coenzyme Q10.
Further reading
- Mortensen SA et al. The effect of coenzyme Q10 on morbidity and mortality in chronic heart failure (Q-SYMBIO). JACC: Heart Failure 2014.[8]
- Al Saadi T et al. Coenzyme Q10 for heart failure. Cochrane Database of Systematic Reviews 2021.[9]
- Xu J et al. Efficacy and safety of coenzyme Q10 in heart failure: a meta-analysis of randomized controlled trials. BMC Cardiovasc Disord 2024.[10]
- Heidenreich PA et al. 2022 AHA/ACC/HFSA Guideline for the Management of Heart Failure. Circulation 2022.[11]