Bleeding DisordersGarlic

Lack of effect of garlic on platelet function in healthy people

It has been suggested that Allium sativum (garlic) inhibits platelet function. If true, this might have positive (used to treat stroke) or negative (bleeding during surgery) effects.

Research from the Vienna Medical University in Austria sheds light on the subject.

First, the details.

  • Whole blood from 18 healthy volunteers was tested before and 5 hours after ingesting Greek tsatsiki (yogurt) with or without (placebo) 4.2 grams of raw garlic (verum).
  • Each volunteer ate both forms of yogurt in random order.
  • Then, the potential long-term effects of garlic were studied in 5 volunteers after eating 4.2 grams of raw garlic daily for a week.

And, the results.

  • Platelet function was normal at the start of the study in all volunteers.
  • Platelet function was not affected by raw garlic.

The bottom line?
The authors concluded, “Dishes containing socially acceptable doses of raw garlic are unlikely to increase the risk of perioperative bleeding.”

These findings support a similar study by researchers at Southern Cross University in Lismore, Australia where one large dose of oil derived from 9.9 grams of garlic had no effect on platelet aggregation (clumping before clotting). The authors concluded, “Garlic oil should not be relied on in persons with conditions in which reductions in platelet aggregation are desired or necessary.”

This is not to suggest that garlic has no effect. A review published this month by Dr. Khalid Rahman from Liverpool John Moores University in the UK reports that in laboratory studies, garlic has many actions: inhibition of cyclo-oxygenase activity and thus thromboxane A2 formation, increased levels of cAMP and cGMP, and a strong antioxidant property that activates nitric oxide synthase (NOS), leading to an increase in platelet-derived NO.

But at in the usual amounts healthy people are likely to eat, none of this amounts to a clinically significant effect on platelet function.

12/8/07 13:36 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at, a complementary and alternative medicine website.