MadSci Network: Botany

Re: Where do most medicinal plants and herbs come from?

Date: Fri Mar 3 14:10:45 2000
Posted By: Joseph E. Armstrong, Faculty, Botany, Illinois State University
Area of science: Botany
ID: 951789132.Bt

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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