There is no doubt that many plants are useful medicinally, just as there is equal certainty that many of them are poisonous. The problem is that these are often the same plants. The vast array of widely available herbal supplements and the equally huge assortment of books on herbal healing reinforce a general sense that natural products are safer than manufactured ones. But the truth is a resounding “sometimes yes and sometimes no.” Herbal medicine is a huge and complicated subject, well worth investigating but by no means something to plunge into incautiously. Things to bear in mind:
- Very few scientifically rigorous studies have been done, largely because almost all such studies are underwritten by drug companies, and herbs, which cannot be patented, could never return the investment involved.
- There is no way for the home gardener to standardize dosage: plants produce different amounts of active chemical agents depending on how and where they are grown, when they are harvested, and the variety characteristics of the particular plant.
- Herbs may interact badly with other drugs, rendering them less effective or more toxic, in unpredictable ways.
- Like other drugs, many herbal toxins are cumulative. Small doses may produce no adverse symptoms but become dangerous in the aggregate.
The don’t-mess-with-in list. A sampling of herbs that have historic reputations as medicinals but are potentially deadly: aconite (Aconitum napellus), deadly nightshade (Atropa belladonna), foxglove (Digitalis purpurea), lily-of-the-valley (Convallaria majalis), lobelia (Lobelia inflata), May apple (Podophyllum peltatum), and pennyroyal (Hedeoma pulegioides and Mentha pulegium both go by this common name, and the oils of both are toxic). Note: for an interesting literary exploration of some of these poisonous plants, check out our upcoming August 9, 2016 blogpost on the natural poisons found in Agatha Christie’s books.
In addition, many well-known herbs appear to be carcinogenic (sassafras, coltsfoot, and comfrey); cause abnormal heart rhythms and/or violent gastrointestinal symptoms (tansy, broom, and blood root); or have other downsides that make freelance experimentation unwise.
The give-it-a-whirl list. A sampling of herbs that are very unlikely to hurt you and may well do some good, assuming you use only small amounts: agrimony (Agrimonia eupatoria), catnip (Nepeta cataria), chamomile (Matricaria recutita and Chamaemelum nobile), echinacea (Echinacea angustifolia), fennel (Foeniculum vulgare), feverfew (Chrysanthemum parthenium), garlic (Allium sativum), hops (Humulus lupulus), peppermint (Mentha x piperita), and valerian (Valeriana officinalis). Be careful with Borage as it absolutely deserves its reputation as a natural laxative; a few leaves go a long way!
In addition, there are herbs that emphatically should NOT be ingested but do have strong healing properties when used externally. First and foremost is aloe, most commonly Aloe vera, which deserves its high reputation as a healer of burns. [Personal side note: I incurred a really, really bad sunburn on my lips in late June of this year — I’m talking second degree burns. Since I have a lovely pot of Aloe growing in my house, I thought I’d smear a little on my lips to make them heal. I have NEVER tasted anything worse in my whole life!! I couldn’t wipe it off fast enough and it took forever for the taste to go away.]
Another healing herb to be used externally is arnica (Arnica montana) which is right up there as an easer of aching muscles, and comfrey (Symphytum officinale) does seem to promote the healing of wounds when applied as a poultice.