Rather than nasty artificial drugs, wouldn’t it be nice if we could just take some herbs and get better? A lot of people think so. Indeed, a large proportion of our drugs and medicines come from plants, or are closely related to plant chemicals. There’s aspirin, morphine, caffeine, cocaine, quinine, and many more. It’s as if plants were going out of their way to help us.
In fact, it’s more like the opposite. Most of these drugs are poisons, produced by the plant to stop animals (that means you) from eating them. As a plant, you don’t want to get eaten, but being, well, rooted to the spot, you can’t exactly run away. All you can do is to make animals not want to eat you. So you fill yourself with noxious, or at least nasty-tasting, chemicals.
By contrast, many plants do want their seeds to get swallowed (but not chewed) by animals and birds, because this ensures that they are spread over a wide area. So they wrap them in delicious, colourful packages. This is why, with only a few exceptions, fruit are sweet and safe while while plant leaves, roots and stems are unpleasant, and often toxic.
In fact, this is quite possibly why the taste of bitter is so unpleasant. Plant toxins are usually alkaloids. Animals must have evolved to find alkaloids nasty, because many of them are poisonous and you survive longer if you don’t enjoy eating poison.
Caffeine, for example, is found in the seeds (“beans”) of the coffee plant, and it makes them taste bitter, to deter herbivores. But those seeds are themselves wrapped in a fruit called the coffee cherry, which is apparently sweet and tasty, although most of them get thrown away in the production of coffee. Coffee wants you to eat the fruit, but swallow the seeds whole, and thereby help spread its DNA. Quinine is one of the bitterest substances on earth, and it’s there to protect the bark of the tree. Nicotine is a bitter insecticide. And so on.
There are some plant chemicals which have medicinal effects which are entirely coincidental: St John’s Wort for example contains some molecules with interesting effects on animals, which are probably quite unrelated to its role in the plant (it absorbs light). It’s also true that plants contain lots of nutrients and the non-toxic ones are, by and large, “healthy” foods, compared to animal products. I say this as a vegetarian. But that doesn’t mean that they cure anything.
So the idea that herbal medicines are “natural”, and thereby safe, is completely backwards. They are natural; that doesn’t make them safe; nature is red in tooth and claw and even the plants are out to get you.