Quick answer

No source checked lists blood clots as a side effect of CoQ10 itself. NCCIH says no serious side effects have been reported, and 13 trials with 602 people reported one digestive effect. The warfarin label does name coenzyme Q10 among products that may decrease warfarin's effect. Ask your pharmacist or doctor first if you take warfarin.^1,2,3

Key facts

NCCIH says no serious side effects of CoQ10 have been reported, and it names warfarin and insulin as medicines CoQ10 may interact with.¹
In 13 trials pooled in a 2022 review, one digestive side effect was reported among the 602 people who took CoQ10.²
The warfarin label lists co-enzyme Q10 among botanicals that may decrease the effects of warfarin and asks for more frequent INR checks when one is started or stopped.³
A small randomized crossover trial in 24 people on stable warfarin found no change in INR or warfarin dose during 4 weeks of 100 mg a day of CoQ10.⁴
MedlinePlus lists coenzyme Q10 among products that may interact with warfarin.⁵

Does CoQ10 cause clots in people who take no blood thinner?

The sources checked do not report blood clots as an effect of CoQ10 on its own. NCCIH's summary says no serious side effects have been reported and lists mild ones, insomnia and digestive upsets, as the kind that may occur. A 2022 systematic review of 13 trials found one digestive side effect among the 602 people who took CoQ10.^1,2

No serious side effects of CoQ10 have been reported.^1,6

That absence is a limit of the evidence as well as reassurance. The review pooled trials of fatigue, not clotting, so it cannot rule out a rare effect, and no source says either way.²

Why does CoQ10 come up with warfarin and clotting?

The sources that do raise a clotting question raise it through one medicine. Warfarin lowers the blood's ability to clot, and doctors adjust the dose by checking a clotting test called the INR. If another product weakens warfarin's effect, the INR falls and the person has less protection against clots than their dose was meant to give.³

The label of warfarin says that drugs, dietary changes and other factors affect INR levels, that INR monitoring should be done more often when starting or stopping other drugs, including botanicals, and that some botanicals may decrease the effects of warfarin, naming co-enzyme Q10, St. John's wort and ginseng. MedlinePlus's page on warfarin goes further and lists coenzyme Q10 among the nonprescription or herbal products that may interact with it.^3,5

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.^1,3,5,6

On the medicine's label

What have studies found about CoQ10 and warfarin?

The evidence is small and mixed. The warfarin label's wording is cautious, and a Danish crossover trial tested the question directly. It gave 24 outpatients on stable, long-term warfarin 100 mg of CoQ10 a day, 100 mg of ginkgo a day and a placebo, each for 4 weeks. The INR stayed stable in every period and the warfarin dose did not change, and the authors concluded CoQ10 did not influence warfarin's clinical effect.⁴

The same abstract says the question began with a few case reports of a decreased response to warfarin in people taking CoQ10. Case reports and a trial of 24 people cannot settle the matter, which is why the label asks for monitoring instead of giving a rule.^3,4

What do the sources not say?

The sources checked do not say whether CoQ10 changes clotting in people who take other anticoagulants, such as apixaban, or antiplatelet medicines such as aspirin. That is not a finding either way, so those questions go to the pharmacist.^3,5

Who should ask a pharmacist or doctor about CoQ10 and clotting?

Anyone taking warfarin, before starting or stopping CoQ10, since the label asks for more frequent INR checks around that change.³
Anyone taking another blood thinner, who should ask the pharmacist what is known about it.³
Anyone with a history of clots, who should tell the prescriber about every supplement, as the warfarin leaflet asks.³
Anyone who uses insulin or is on cancer treatment, since NCCIH names these as other cautions.¹

Questions people ask

Can coq10 cause blood clots?

The sources checked do not list clots as a side effect of CoQ10 on its own. They do say CoQ10 may weaken warfarin, so ask your pharmacist or doctor first if you take it.^1,3

Does coq10 thin the blood?

NCCIH does not describe CoQ10 as a blood thinner. It says CoQ10 may interact with warfarin, and the warfarin label says co-enzyme Q10 may decrease warfarin's effects. Ask your pharmacist about your medicines.^1,3

Does coq10 raise INR or lower it?

The warfarin label lists co-enzyme Q10 among botanicals that may decrease warfarin's effects, which would be expected to lower INR. A small 4-week trial of 100 mg a day found INR stable. Ask your pharmacist about monitoring.^3,4

Does coq10 cause bleeding?

No source checked lists bleeding as a side effect of CoQ10. NCCIH says no serious side effects have been reported. If you take warfarin or another blood thinner, ask your pharmacist before starting.¹

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