Based on chondroitin’s chemical similarity to the anticoagulant drug heparin, it has been suggested that chondroitin might have anticoagulant effects as well. There are no case reports of any problems relating to this, and studies suggest that chondroitin has at most a mild anticoagulant effect.19 Nonetheless, prudence suggests that chondroitin should not be combined with heparin except under physician supervision.

The herb garlic (Allium sativum) is taken to lower cholesterol, among many other proposed uses.

Because garlic has a blood-thinning effect itself, it might be dangerous to combine garlic with heparin.1,2

Two cases have been reported in which the combination of garlic and the blood-thinner warfarin doubled the time it took for blood to clot.3 Though warfarin thins the blood in a different way than heparin, there are concerns that garlic might interact similarly with heparin.

The herb ginkgo (Ginkgo biloba) has been used to treat Alzheimer's disease and ordinary age-related memory loss, among many other conditions.

Ginkgo thins the blood by reducing the ability of blood-clotting cells called platelets to stick together.4 Because case reports have implicated use of Ginkgo biloba in the development of serious bleeding abnormalities,5,6,7 combining ginkgo with heparin might be expected to intensify the danger.

PC-SPES is an herbal combination that has shown promise for the treatment of prostate cancer. One case report suggests that PC-SPES might increase risk of bleeding complications if combined with blood-thinning medications.18

The supplement phosphatidylserine is promoted to treat Alzheimer's disease and ordinary age-related memory loss.

A test tube study suggests that phosphatidylserine might amplify heparin's blood-thinning effects.8 If this effect were to occur inside the body, it could increase the risk of abnormal bleeding. If you receive heparin, make sure you check with your doctor before taking phosphatidylserine.

Policosanol, derived from sugarcane, has been taken for hyperlipidemia and intermittent claudication.

Human trials suggest that policosanol makes blood platelets more slippery, an action that could potentiate the blood-thinning effects of heparin, possibly causing a risk of abnormal bleeding episodes.9 A 30-day double-blind placebo-controlled trial of 27 individuals with high cholesterol levels found that policosanol at 10 mg daily markedly reduced the ability of blood platelets to clump together.10 Another double-blind placebo-controlled study of 37 healthy volunteers found evidence that the blood-thinning effect of policosanol increased as the dose was increased—the larger the policosanol dose, the greater the effect.11 Yet another double-blind placebo-controlled study of 43 healthy volunteers compared the effects of policosanol (20 mg daily), the blood-thinner aspirin (100 mg daily), and policosanol and aspirin combined at these same doses.12 The results again showed that policosanol substantially reduced the ability of blood platelets to stick together, and that the combined therapy exhibited additive effects.

Based on these findings, you should not combine heparin and policosanol except under medical supervision.

Test tube studies suggest that high amounts of vitamin C may reduce the blood-thinning effect of heparin.13 However, it is not clear whether the interaction is significant enough to make a practical difference.

The herb white willow (Salix alba), also known as willow bark, is used to treat pain and fever. White willow contains a substance that is converted by the body into a salicylate similar to aspirin.

Since combining aspirin with heparin increases the risk of abnormal bleeding, it would be advisable not to combine white willow with heparin.

Based on their known effects or constituents, the following herbs and supplements might not be safe to combine with heparin, though this has not been proven: bromelain (in the fruit and stem of pineapple, Ananas comosus), papaya (Carica papaya), chamomile(Matricaria recutita), Coleus forskohlii, danshen (Salvia miltorrhiza), devil's claw(Harpogophytum procumbens), dong quai(Angelica sinensis), feverfew(Tanacetum parthenium), ginger(Zingiber officinale), horse chestnut(Aesculus hippocastanum), red clover(Trifolium pratense), reishi(Ganoderma lucidum), mesoglycan, fish oil, OPCs (oligomeric proanthocyanidins), and vitamin E.

High doses or long-term use of heparin may interfere with the proper handling of vitamin D by the body;14 because vitamin D is needed for calcium absorption and utilization, this may in turn lead to bone loss and osteoporosis. Additionally, heparin may directly interfere with bone formation.15

This interaction is of special concern during pregnancy, when there is a greater calcium demand and diminished levels of a hormone that pushes calcium into bones. In fact, there have been several reports of fractured and collapsed vertebrae in pregnant women on heparin therapy.16,17

Supplementary calcium and vitamin D may help prevent heparin-induced osteoporosis. It might also be advisable to have your bone density checked during long-term heparin therapy.