Supplements That Thin Blood: What You Need to Know

Medically Reviewed by Nayana Ambardekar, MD on June 20, 2024
4 min read

Lots of people take supplements, like fish oil, melatonin, or ginkgo. The FDA doesn’t regulate these the same way they do prescription and over-the-counter drugs. But that doesn’t mean they’re less powerful.

Some of them can thin your blood. It’s generally not a big deal if you’re healthy. You just might bleed a little more if you get a cut or a bruise. But there are times when that can be dangerous. Here's what you need to know.

Warfarin is one of the commonly used blood thinners. It slows the clotting process. Doctors usually prescribe it to help lower your risk of:

It’s not a good idea to take this drug with a supplement that thins blood. It raises your chances of severe bleeding inside and outside your body.

If your doctor wants you to start using warfarin, you might wonder if you can take a supplement instead. But there’s no good scientific evidence that shows they work as well as prescription drugs.

Always talk to your doctor before using any supplement. They’ll tell you if it’ll affect any medications you’re taking.

It's important to tell your doctor about any supplements you're taking if you have a surgery planned. Even if it's something minor like getting a tooth pulled. That’s because you could end up bleeding heavily during the procedure if the supplement thins your blood or affects clotting.

Most of the time, your surgeon will ask you to stop taking prescription blood thinners and blood-thinning supplements for at least 1 week before your surgery.

Research shows several supplements may affect how well your blood can form clots. For many of these, it’s not clear how much of the supplement is needed to affect clot formation. Some of these include:

Aloe. In one case, a woman taking an aloe supplement bled heavily after oral surgery. There's also a risk of bleeding if you take aloe with nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin or ibuprofen.

Cranberry. There are documented cases of cranberry supplements interacting with warfarin. This can lead to bleeding.

Feverfew. Lab studies of platelets show it can affect their ability to stick together and form clots.

Fish oil.  Although research shows that fish oil may cause platelets from sticking together, there seems to be no increased bleeding risk.”

Garlic. Animal and human studies show it can slow blood clotting and lead to bleeding.

Ginger. One study found high doses of ginger affected clotting. More research is needed, but there’s also evidence it can raise your risk of bleeding if you're taking warfarin.

Ginkgo. Research shows it can slow clotting. It’s also led to bleeding in people who took it alone or with NSAIDs.

Meadowsweet. There are no reports of meadowsweet interacting with warfarin or NSAIDs. But it has a compound called salicylate that affects how well platelets can stick together.

Turmeric. Curcumin, one of turmeric's active ingredients, has antiplatelet effects.

White willow. This supplement has aspirin-like effects in the body. That means it can keep platelets from sticking together. There's no documented evidence of it interfering with warfarin.

Chamomile. This herb contains the compound coumarin. Warfarin has a man-made version of coumarin in it. But more research is needed to find out if it has any effect on blood clotting.

Fenugreek. Like chamomile, fenugreek contains coumarin. But more research is needed to find out if it has any effect on blood clotting.

Red clover. There's limited research about this supplement, but it also has coumarin. But more research is needed to find out if it has any effect on blood clotting.

Dong quai. It contains several compounds that come from coumarin. It has been shown to worsen bleeding in people taking warfarin.

Evening primrose oil. Animal studies show it slows the clotting process and stops platelets from sticking together. So it may make you bleed more during and after surgery, and when taken with warfarin or NSAIDs. More research in humans is needed.

Ginseng. Some lab studies show it can thin the blood, but more research is needed to know for sure.

Call your doctor right away if you have any of these signs of heavy internal (inside your body) bleeding:

  • Bleeding during your period that’s heavier than normal
  • Red or brown pee
  • Poop that’s red or looks like tar
  • Nose or gum bleeding that doesn’t stop quickly
  • Brown or bright red vomit
  • A severe headache or stomachache
  • Unusual bruising
  • A cut that won’t stop bleeding
  • Dizziness or weakness

You should also call them if you cough up anything red-colored or fall and bump your head.