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Medicines and supplements

Supplements to avoid with blood thinners

Written by the Full Measure editorial team, which sells supplements. Approved for publication by the Full Measure owners. Updated 2026-10-13.

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

Quick answer

Ask your pharmacist or doctor before combining. Official sources document 8 supplements for blood thinners: omega-3, vitamin E, vitamin K, niacin, melatonin, echinacea, CoQ10 and resveratrol. The sources are medicine labels, NIH, NCCIH, LiverTox and MedlinePlus, and each entry below says how it is known.^1,2,3,4,5

Key facts

MedlinePlus says blood thinners may interact with certain foods, medicines, vitamins and alcohol, and asks you to make sure your provider knows every supplement you use.¹
Vitamin K works against warfarin and similar medicines, so NIH and the warfarin label advise keeping vitamin K intake about the same from day to day.^6,7
Omega-3, vitamin E and niacin are each documented as able to affect platelets or clotting tests, and the sources ask for monitoring or a conversation first.^8,9,10
The warfarin label names echinacea and coenzyme Q10 among botanical products that can change how warfarin works, and asks for more frequent INR checks whenever a botanical is started or stopped.^5,11
Melatonin and resveratrol have thinner documentation: NCCIH asks for medical supervision with melatonin, and NIH's LiverTox lists a possible interaction for resveratrol.^3,4

What do blood thinners do, and why do supplements matter?

MedlinePlus describes blood thinners as medicines that keep clots from forming. They do not dissolve a clot you already have, but they can stop it from growing. Anticoagulants such as heparin and warfarin slow the body's clot-making process, while antiplatelets such as aspirin and clopidogrel stop platelets from clumping together.¹

Bleeding is the most common side effect of the group, so anything that nudges clotting in either direction deserves a conversation. The same page says these medicines may interact with certain foods, medicines, vitamins and alcohol, and that your health care provider needs the full list of what you use.¹

The entries below are not equal in weight. Some come from a medicine's own label, one rests on case reports, and two are reasoned from how the supplement and the medicine work. They are grouped by what each supplement is documented to do, and every card shows its severity tag and its basis.

Which supplements can change bleeding risk or clotting tests?

Your doctor may want to check on you

High doses of omega-3s may cause bleeding problems when taken with warfarin or other anticoagulants, and fish oil can have antiplatelet effects at high doses. Fish oil might also prolong clotting time, measured as INR, in people taking warfarin. The label of a prescription omega-3 medicine says people who also take an anticoagulant or an antiplatelet medicine should be monitored periodically.^2,8,12

On the medicine's label

The omega-3 card is the only one on this page tagged monitor instead of ask first. Its backbone is the label of a prescription omega-3 medicine, which asks for periodic monitoring when an anticoagulant or an antiplatelet medicine is also taken.¹²

Ask your pharmacist or doctor first

Vitamin E can slow the clumping of platelets and work against the clotting factors that depend on vitamin K. Taking large doses with an anticoagulant or antiplatelet medicine, such as warfarin, can therefore increase the risk of bleeding, especially when vitamin K intake is low. NIH says the amount needed to cause a clinically significant effect is not known.^9,13

Expected from how the two work, not shown in studies

NIH says the amount of vitamin E needed to cause a clinically significant effect is not known. That is a gap in the evidence, not a reassurance, and this card is reasoned from mechanism instead of being printed on a label.^9,13

Ask your pharmacist or doctor first

The prescription niacin label reports small, dose-related drops in platelet count and rises in prothrombin time, a clotting test, and advises caution and close monitoring of both in people taking anticoagulants. NIH notes that nicotinamide at 500 mg a day or more can cause easy bruising and more bleeding from wounds.^10,14

On the medicine's label

The label behind the niacin card is for a prescription niacin tablet, and NIH's sentence is about high amounts of nicotinamide. The sources checked do not say how ordinary store-bought niacin, B-complex or multivitamin products compare, so bring the actual bottle to the pharmacy.^10,14

Does vitamin K interfere with blood thinners?

Vitamin K is different from the rest of the page. Instead of adding to a blood thinner it pulls the other way, and the sources focus on consistency from day to day rather than on avoiding the vitamin.^6,7

Ask your pharmacist or doctor first

Warfarin and similar blood thinners work by blocking vitamin K. A sudden rise in vitamin K from food or supplements can weaken their effect and raise the chance of a blood clot, and a sudden drop can strengthen it and cause dangerous bleeding. NIH and the warfarin label advise keeping vitamin K intake about the same from day to day. NIH names warfarin and similar medicines used in Europe (phenprocoumon, acenocoumarol and tioclomarol), not blood thinners that work in other ways.^6,7,15,16

On the medicine's label

NIH names warfarin and related medicines used in Europe, not blood thinners that work in other ways. If you take a newer anticoagulant or an antiplatelet medicine, the vitamin K sources here do not speak to you directly. That is not a finding either way, so ask your pharmacist.¹⁵

Which herbal supplements are named for blood thinners?

Echinacea, coenzyme Q10 and resveratrol reach this page through the warfarin label, MedlinePlus and NIH's LiverTox. Warfarin is the anticoagulant most of those sources name, so the cards below say warfarin where the source does and anticoagulants where it does.^4,11,17

Ask your pharmacist or doctor first

The warfarin label names echinacea among botanicals that can interact with warfarin through CYP450 liver enzymes, and asks for more frequent INR checks whenever a botanical is started or stopped. MedlinePlus also lists echinacea among herbal products that may interact with warfarin.^11,17

On the medicine's label

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.^5,18,19,20

On the medicine's label

Ask your pharmacist or doctor first

NIH's LiverTox database lists a possible interaction between resveratrol and anticoagulant blood thinners. The warfarin label asks for more frequent INR checks whenever a botanical product is started or stopped, and MedlinePlus says some supplements may raise the risk of bleeding with warfarin.^4,21,22

Expected from how the two work, not shown in studies

MedlinePlus's warfarin page names more herbal products than these three: garlic, ginkgo biloba, ginseng, goldenseal and St. John's wort. They have no card here, and the warfarin page on this site goes through the list.²³

The label's request for more frequent INR checks covers any botanical product, named or not, so a product missing from a list is not a product cleared by it.^11,21

Is melatonin on the list for blood thinners?

Ask your pharmacist or doctor first

NCCIH says people taking blood thinner medicines need to be under medical supervision when taking melatonin. A Cochrane review noted case reports suggesting that people taking warfarin may come to harm from melatonin, and called for the possible interaction to be studied.^3,24

Reported in studies

This is the thinnest card on the page. NCCIH's advice about medical supervision carries most of the weight, and the Cochrane review's note about case reports adds a call for study, not a finding. What the sources describe is an open question rather than a settled one.^3,24

What do ask first, monitor, on the label and expected mean?

Each card carries two tags. The severity tag is the page's plain-word level of concern: omega-3 is monitor, and the other seven are ask first. The basis tag says how the interaction is known: on the label for omega-3, echinacea, vitamin K, CoQ10 and niacin, in studies for melatonin, and expected from how the two work for vitamin E and resveratrol.

The eight documented supplements, by severity tag and basis
Supplement	Severity tag	How it is known
Omega-3	Monitor	On the label
Vitamin E	Ask first	Expected from how the two work
Echinacea	Ask first	On the label
Vitamin K	Ask first	On the label
Resveratrol	Ask first	Expected from how the two work
CoQ10	Ask first	On the label
Niacin	Ask first	On the label
Melatonin	Ask first	In studies

No card carries the severity avoid. Despite the common search wording, the sources checked ask for a conversation or for monitoring, and this page does not tell anyone to start or stop a supplement. That decision belongs to the person who prescribes the thinner.

What to ask your pharmacist before adding a supplement to a blood thinner

For a supplement that is not on this page, the sources checked do not address it. That is not a finding either way, so ask your pharmacist.

Is my blood thinner an anticoagulant such as warfarin, or an antiplatelet medicine?¹
Will I need an extra INR or other clotting test if I start or stop a supplement?¹¹
Do any products I already take, such as a fish oil, multivitamin or B-complex, contain omega-3, vitamin E, vitamin K or niacin?
Which teas, powders and herbal blends in my cabinet count as botanical products?

Bring every bottle. MedlinePlus lists the signs of serious bleeding to report: menstrual bleeding much heavier than normal, red or brown urine, red or black bowel movements, gum or nose bleeds that do not stop quickly, and brown or bright red vomit.¹

Questions people ask

Which supplements should I avoid if I'm on blood thinners?

Official sources document 8 supplements to raise with your pharmacist first: omega-3, vitamin E, vitamin K, niacin, melatonin, echinacea, CoQ10 and resveratrol. This page does not tell you to start or stop anything, because that decision belongs to your pharmacist or prescriber.^1,3,8

What vitamins should you not take while on blood thinners?

Three vitamins are documented: E, K and niacin. NIH says people on warfarin should keep vitamin K steady, and the sources ask for monitoring or a conversation before changing vitamin E or niacin. Ask your pharmacist before you start or stop any of them.^6,9,10

What supplements can you take with blood thinners?

No source checked gives a list of supplements cleared for use with blood thinners. For any supplement not on this page, the sources checked do not address it. That is not a finding either way, so ask your pharmacist.¹

Which herbal supplements are on the list to avoid with blood thinners?

Echinacea is named by the warfarin label and MedlinePlus, CoQ10 by the label, NCCIH and MedlinePlus, and resveratrol by NIH's LiverTox. The label asks for more frequent INR checks when any botanical product is started or stopped.^4,11,17,18

What can you not take with blood thinners?

MedlinePlus says blood thinners may interact with certain foods, medicines, vitamins and alcohol. Its warfarin page also names aspirin and anti-inflammatory pain relievers such as ibuprofen and naproxen. Ask your pharmacist about anything you buy over the counter.^1,23

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Sources

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