Pentoxifylline, a drug that makes the blood less "sticky," is used to increase blood circulation in conditions such as intermittent claudication (a possible complication of atherosclerosis in which impaired blood circulation causes severe pain in calf muscles during walking or exercising).

Possible Harmful Interaction

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.16 Nonetheless, prudence suggests that chondroitin should not be combined with pentoxifylline except under physician supervision.

Possible Harmful Interaction

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

One of the possible side effects of garlic is an increased tendency to bleed.1,2 Therefore, you should not combine garlic and pentoxifylline except under medical supervision.

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

Ginkgo appears to reduce the ability of platelets (blood-clotting cells) to stick together.3 Several case reports suggest that this blood-thinning effect of ginkgo may be associated with an increased risk of serious abnormal bleeding episodes in individuals taking the herb.4,5,6

Because of these risks, you should not combine ginkgo and pentoxifylline without physician supervision.

Possible Harmful Interaction

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.11 Subsequent evidence has indicated that PC-SPES contains the strong prescription blood-thinner warfarin (Coumadin), making this interaction inevitable.15

Possible Harmful Interaction

The supplement policosanal is used to reduce cholesterol levels. It also intereferes with platelet clumping, creating a risk of interactions with blood-thinning drugs.

For example, 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.8 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.9 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.10 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 pentoxifylline and policosanol except under medical supervision.

Possible Harmful Interaction

One study suggests that reishi impairs platelet clumping.12 This creates the potential for an interaction with any blood-thinning medication.

Possible Harmful Interaction

The substance vinpocetine is sold as a dietary supplement for the treatment of age-related memory loss and impaired mental function.

Vinpocetine is thought to inhibit blood platelets from forming clots.13 For this reason, it should not be combined with medications or natural substances that impair the blood’s ability to clot normally as this may lead to excessive bleeding. One study found only a minimal interaction between the blood-thinning drug warfarin (Coumadin) and vinpocetine, but prudence dictates caution anyway.14

Possible Harmful Interaction

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 the blood-thinner aspirin. For this reason, white willow might add to the effects of pentoxifylline, possibly thinning the blood too much.

It may be advisable to avoid white willow while taking pentoxifylline except under medical supervision.

Possible Harmful Interaction

Herbs and supplements that impair the blood's ability to coagulate (clot) might add to the effects of pentoxifylline, possibly increasing the risk of excessive bleeding. This includes most prominently vitamin E.

Numerous other substances could conceivably present this risk, including mesoglycan, bromelain (from the fruit and stem of pineapple, Ananas comosus), chamomile(Matricaria recutita), Coleus forskohlii, danshen (Salvia miltorrhiza), dong quai(Angelica sinensis), feverfew(Tanacetum parthenium), fish oil, ginger(Zingiber officinale), horse chestnut(Aesculus hippocastanum), OPCs (oligomeric proanthocyanidins), papaya (Carica papaya), and red clover(Trifolium pratense).