One of my favourite phytochemistry groups when I was studying naturopathy were the coumarins. I find it enchanting when the presence of a plant chemical can be guessed at from the taste, smell or some other observable factor, such as the soapiness of plants containing saponins.

Coumarins are plant chemicals that smell like freshly mown grass or newly cut hay, because this is the chemical released by coumarin-rich plants when they are injured. Most coumarins are found in members of the Fabaceae and Poaceae families (legumes and grasses), but some are found in members of the nightshade family, the apiaceae family and a diverse range of plants ranging from poppies through to grapefruit.

Coumarins in general are antioxidant and anti-inflammatory, but what makes them really shine is their ability to tone and strengthen veins and lymphatic vessels. As a result, plants and herbs rich in coumarins are often used to treat fluid retention, varicose veins and haemorrhoids. A really good example of this is horse chestnut, which herbalists use for venous insufficiency, varicose veins, haemorrhoids, lymphoedema, and for reducing the risk of deep vein thrombosis. But as Lisa Ganora says, the coumarins in horse chestnut are working hand-in-hand with another phytochemical called saponins to achieve this outcome. And who knows how many more? The therapeutic action of a plant is a complex, whole-plant affair, after all.

Coumarins often get singled out as being unsafe for use alongside the anticoagulant drug Warfarin, because of their blood-thinning activity, but in actual fact, their blood thinning action isn’t particularly strong. The confusion seems to have arisen from the fact that Warfarin was “structurally patterned”, as Lisa Ganora so eloquently puts it, on dicoumarol, a fungal metabolite that forms in mouldy or poorly dried coumarin-rich plant material. The class of drugs to which Warfarin belongs might be referred to within the medical industry as “coumarins”, but they are definitely not coumarins!

The material for this article comes my training as a naturopath and from one of my favourite new reference books: ‘Herbal Constituents- foundations of phytochemistry’, by Lisa Ganora, (a holistic approach for students and practitioners of botanical medicine.) 

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