Nature’s pharmacy? “Medicinal” plants in the garden

Photo: Echinacea purpurea; credit: Jamie Heard

Note: This is a science outreach piece belonging to a series I wrote for the newsletter of the Fredericton Botanic Garden. I’d be happy to see it modified for use elsewhere and so am posting the text here under a CC BY-SA 4.0 license . If you use it, though, I’d appreciate hearing where and how.

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You don’t need to spend long on the Web, or talking with family and friends, to hear about the wonderful potential of plants to treat human illness. The medicinal value of plant extracts is a major theme in “alternative”, “naturopathic”, “traditional”, and “herbal” medicine – and indeed, in just plain medicine, because many of the drugs we use to restore our health have their origins in the biochemical machinery of plants.

Look around the Botanic Garden – or your own garden – and you’ll see plenty of plants with historical, and often continued, medicinal uses. To pull just a few examples from the Fredericton Botanic Garden’s collections: daylily (Hemerocallis) extracts have been used to treat arsenic poisoning and fever; coneflower (Echinacea) is widely taken to alleviate cold and flu symptoms; speedwell (Veronica spicata) is said to relieve coughs and treat skin conditions; and bellflower or tickseed (Coreopsis verticillata) is a diuretic. Many (not all) such reported effects are real, and that’s no surprise: plant-synthesized chemicals interact with the human body in many, many ways. Consider, among familiar medicines, aspirin (from willow bark), digitalin (foxglove), atropine (nightshade), quinine (cinchona tree), and scopolamine (jimsonweed); or think about “recreational” compounds such as caffeine (coffee) and nicotine (tobacco), flavour compounds such as capsaicin (peppers) and myrcene (bay leaf), and, of course, poisons such as cyanide (cassava) and ricin (castor bean).

So why do plants make so many chemicals that interact with our animal biochemistry in so many ways, both helpful and harmful? Most such chemicals seem to play no purpose in plant metabolism, and were once thought to be waste products or accidental byproducts. But in fact, they are no accident. Plants have evolved thousands of chemicals as inducements in their animal partnerships and as weapons in their animal wars. Some are attractants, like isoamyl acetate (the fragrance of a ripe banana), which evolved to recruit animals to eat fruits and thus disperse seeds. Others are feeding repellants: capsaicin in hot peppers binds mammalian pain receptors but not bird ones, and has evolved because birds disperse pepper seeds but mammals kill them. Still other chemicals kill attacking insects, or disrupt their development, like the precocenes in flossflower (Ageratum) that mimic insect hormones and cause premature metamorphosis of insects attacking that plant. Once effects on animal biochemistry have evolved, it’s a short step to our exploiting these effects to tweak our own biochemistry medicinally.

So: is there a pharmacy in the garden? Well, yes and no. There’s no question that many plants contain compounds that, properly used, can benefit human health. But a big note of caution is in order. I often hear people say that botanical medicines are safe because they’re “natural”, and nothing could be further from the truth! After all, digitalin, cocaine, and belladonna are all natural, and I wouldn’t take a chance with any of them. When you use a botanical medicine, there are really two possibilities. It might not work – in which case it is indeed safe, but only because it’s having no effect. Or it might work – in which case it makes a significant change in your body’s biochemistry, may interact with other medicines you’re taking, and probably isn’t something you should be rushing into. The bottom line is that plant-based medicines can be either life-threatening or life-saving; and the difference comes from the extensive scientific research that you access when you consult a medical professional. So (for many reasons) please don’t chew our shrubs!

© Stephen Heard (sheard@unb.ca) May 21 2015 but licensed CC BY-SA 4.0 .

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