|MadSci Network: Botany|
Where do most medicinal plants and herbs come from? Well, I donít know actually what this question is asking. Is this about why medicinal plants exist? Or is it where medicinal plants come from taxonomically, that is, what groups of plants provide medicinals? Or where do medicinal plants come from geographically or historically? Possibly itís about how people have discovered medicinal plants? Let me respond to the last question since I think it the most likely. Let me explain a couple of things that you need to know to understand what I will tell you next. First, plants are complex biochemical factories that can synthesize all the molecules that they need for a wide variety of functions. Some of those molecules are used for interacting with other organisms, attracting pollinators, seed dispersers, and other beneficial organisms, and repelling or defending themselves against other organisms that will do them harm. Like all animals humans must obtain prefabricated complex molecules (food) to use for raw materials and energy because animals cannot synthesize all the molecules they need. And either directly or indirectly through eating and being eaten, humans get all their food from plants. In our long human quest for food, people in primitive cultures experimented with virtually all plant resources as possible food. This trial and error experimentation sometimes discovered other useful plants or plant products including toxic plants. The knowledge of such plants becomes cultural knowledge allowing people to learn without having to experiment because such experiments with plants can be very risky. Without a knowledge of botany, most people would not last long in nature trying to find safe, nutritious food by trial and error because with some plants you only get one mistake. Out of the 300,000 or so species of plants, that some will produce molecules of medicinal value is not surprising since many are designed to interact with animals. Toxic plants contain substances that when consumed produce a non-nutritional physiological change in the consumer, an intoxication. Some intoxications are harmful (poisons), some are beneficial (medicinal), and some are perplexing (hallucinogens). Some toxic plants can be all three at once depending on dosage. Some intoxications stimulate the central nervous system (like caffeine or nicotine), and some intoxications depress the central nervous system (ethanol and narcotic pain killers like morphine). So little by little people learned about what these various toxic plants did, and science figured out how many of the do what they do, and thus made more effective medicines. So medicinal plants contain a toxic substance that has proven to be of some therapeutic value in treating diseases, disorders, or some other physical problem (injury, infection). Herbs is a very general term that can mean non-woody plant, a common fragrant seeds and leaves, as in herbs and spices, or medicinal plant. However, before someone becomes overly enthusiastic about medicinal plants, folk knowledge of medicinal plants has some problems. While traditional cultural knowledge has found many medicinal plants, it also believes there is value in many useless plants as well (a false positive). This is because no matter what you do people often get better. Suppose every time you get a cold, I tell you a peanut butter chest rub will make you better. And sure enough you get over the cold every time, but did this prove peanut butter helped? Not at all. Similar treatments have produced unfounded beliefs in the value of many herbal remedies. Cultural knowledge also has no understanding of the mechanism of the medicine and only very crude knowledge of effective dosage. Plants vary one to another, from time to time, and place to place. A plant collected one year in one place may have produced very different amounts of some toxic chemical, but an herb collector would have no way of knowing if the dosage is too little or too great. In fact many herbal remedies fail to provide an effective dosage, and so are useless. Medicinal plants must be studied scientifically, the effective toxic substance identified, and an effective dosage determined to make an effective medicine. Many such medicines exist, for example aspirin or quinine were both isolated from bark. However many things sold as herbal remedies have failed to yield positive results when tested for effectiveness. Echinacea, a coneflower, last yearís top selling herbal cold remedy has not demonstrated any effectiveness in clinical trials. Why would so many people pay for a useless remedy? Advertising based on testimonials, which in turn are based on personal experience. But just like peanut butter chest rubs, getting better from a cold after taking Echinacea did not prove it effective even if people thought so. There is also the placebo effect. People who think they are taking an effective remedy respond positively even if the remedy is just a sugar pill, a placebo. In clinical trials placebos are used as an experimental control to see if people are just fooling themselves. So many effective medicinal plants exist. But aspirin is much more effective at painkilling than chewing on white willow bark. Just because one herbal remedy is good does not mean they all are, and many useless remedies are sold to many people. People using herbal remedies may do no more than waste their money, but if they fail to seek effective medical treatment as a result, then great harm can be done. Hereís another example. I have read several times that garlic can prevent cancer and garlic tablets are sold as an herbal remedy. In one experiment using about 2 dozen mice, a crude enzyme extract of garlic injected into the mice reduced their skin tumors. Now this suggests that an anti-tumor substance exists in this extract of garlic, but this is not prevention either. An extract injection and eating garlic do not do the same thing. Enzymes are proteins and they get digested when ingested, so how would they do anything to any tumor we might have? Eating garlic is not bad, but there is no evidence it does anything to prevent cancer. Itís peanut butter again; if you eat lots of garlic and do not get cancer have you proven it works? Not at all. So if you still want to believe, it would be much cheaper to buy garlic powder or garlic at the grocery rather than paying much more for garlic packaged as an herbal remedy. This type of exaggeration and extrapolation are quite irresponsible, but while I regularly point out the problems and lack of evidence for many alternative therapies, I also regularly get angry letters from believers. It's as if I am the one who tells them there is no Santa Claus. So toxic plants provide many substances of medicinal value, but we must remain careful about believing every benefit claimed particularly when there has been insufficient study or the research conducted has demonstrated no value. Many common books about medicinal plants pass along folklore as established fact when many claims remain quite questionable. So do not substitute belief for knowledge. Do your homework before deciding whether an herbal remedy may be useful.
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