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Ingredient guide

CoQ10 side effects: what studies report

Written by the Full Measure editorial team, which sells supplements. Approved for publication by the Full Measure owners. Updated .

Drafted with AI assistance from the sources listed below. How we write these

Quick answer

No serious side effects of CoQ10 have been reported. The usual ones are mild: trouble sleeping at 100 mg a day or more, nausea, heartburn and an upset stomach. CoQ10 can also make the blood thinner warfarin less effective, so ask first if you take it.1,2,3

Key facts

  • Stomach complaints did not climb with the dose: a review of trials found them as common at 60 mg a day as at 1,200 mg.4
  • Across 13 trials, one digestive side effect was reported among 602 people taking CoQ10.5
  • No official upper limit exists, and a trade-group risk assessment named 1,200 mg a day the observed safe level.4
  • Rash, headache, dizziness and sensitivity to light have also been reported.2

The common ones

No serious side effects of CoQ10 have been reported.1,2

Doses of 100 mg a day or more have caused mild trouble sleeping in some people.1,2

Digestive upsets can occur, including nausea, heartburn and pain in the upper stomach.1,2

Other reported side effects include rash, headache, dizziness, irritability, sensitivity to light and tiredness.2

If CoQ10 keeps you awake, taking it earlier in the day is a common suggestion, though no study cited here tested it.

Do side effects rise with the dose?

In a review of clinical trials, nausea and other stomach effects were no more common at 1,200 mg a day than at 60 mg.4

Across 13 trials pooled in a 2022 review, one digestive side effect was reported among the 602 people who took CoQ10.5

Raised liver enzymes have been seen in people taking 300 mg a day for long periods, without liver damage.2

No official upper intake level exists for CoQ10. A published risk assessment found strong evidence of safety in clinical trials at intakes up to 1,200 mg a day and named that the observed safe level; its authors worked for a supplement industry trade association. An NIH summary reports no serious toxicity.2,4

Medicines CoQ10 can affect

Ask your pharmacist or doctor first

CoQ10 may make the blood thinner warfarin less effective. The warfarin label lists coenzyme Q10 among products that may decrease warfarin's effects and advises more frequent INR checks when starting or stopping them. NIH's complementary health center and MedlinePlus also list the interaction.1,2,3,6

On the medicine's label

Your doctor may want to check on you

CoQ10 may interact with insulin. An NIH summary says it can lower the amount of insulin people with diabetes need, so tell whoever prescribes your insulin before starting it.1,2

Expected from how the two work, not shown in studies

Statins act the other way round, lowering CoQ10 in the blood. NIH's complementary health center finds that the overall evidence does not show CoQ10 reducing muscle pain caused by statins, so talk to your prescriber rather than adding CoQ10 on your own.1,7

According to NIH's complementary health center, CoQ10 may not be compatible with some cancer treatments, so ask your oncology team before taking it.1

Who should ask a doctor first

  • Anyone taking warfarin or another blood thinner
  • Anyone using insulin or another medicine that lowers blood sugar
  • Anyone being treated for cancer
  • Anyone on a statin who has muscle pain, before changing anything
  • Anyone pregnant, nursing or under 18, or who has trouble sleeping

The sources here do not report on CoQ10 in pregnancy or breastfeeding, which is why the advice is to ask first.

Questions people ask

Is CoQ10 safe to take daily?

Daily use is how the trials gave it, for weeks to months. No serious side effects have been reported, and a trade-group risk assessment found strong evidence of safety up to 1,200 mg a day, though no official upper limit has been set.1,4

Is CoQ10 safe for diabetics?

CoQ10 may interact with insulin, and an NIH summary says it can lower the amount of insulin people with diabetes need. If you have diabetes, ask whoever manages your treatment before starting it.1,2

Do women get different side effects?

Neither NCCIH nor the NIH summary separates side effects by sex. Pregnancy and nursing are reasons to check with a doctor first.1,2

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Sources

  1. National Center for Complementary and Integrative Health (NIH). Coenzyme Q10. Last updated January 2019. Opened 2026-10-07.
  2. PDQ Integrative, Alternative, and Complementary Therapies Editorial Board. Coenzyme Q10 (PDQ): Health Professional Version. National Cancer Institute. Updated October 31, 2024. Opened 2026-10-07.
  3. Warfarin sodium tablets: prescribing information (Amneal Pharmaceuticals). DailyMed, U.S. National Library of Medicine. Published June 3, 2026. Opened 2026-10-07.
  4. Hathcock JN, Shao A. Risk assessment for coenzyme Q10 (Ubiquinone). Regul Toxicol Pharmacol. 2006;45(3):282-288. Opened 2026-10-01.
  5. Tsai IC, Hsu CW, Chang CH, Tseng PT, Chang KV. Effectiveness of Coenzyme Q10 Supplementation for Reducing Fatigue: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Front Pharmacol. 2022;13:883251. Opened 2026-10-01.
  6. MedlinePlus. Warfarin. U.S. National Library of Medicine. Last revised March 15, 2026. Opened 2026-10-07.
  7. Qu H, Meng YY, Chai H, et al. The effect of statin treatment on circulating coenzyme Q10 concentrations: an updated meta-analysis of randomized controlled trials. Eur J Med Res. 2018;23(1):57. Opened 2026-10-07.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.