David Kroll’s recent article on thunder god vine is a great example of what can be learned by using science to study plants identified by herbalists as therapeutic. The herbalists’ arsenal can be a rich source of potential knowledge. But Kroll’s article is also a reminder that blindly trusting herbalists’ recommendations for treatment can be risky.

Herbal medicine has always fascinated me. How did early humans determine which plants worked? They had no record-keeping, no scientific methods, only trial and error and word of mouth. How many intrepid investigators poisoned themselves and died in the quest? Imagine yourself in the jungle: which plants would you be willing to try? How would you decide whether to use the leaf or the root? How would you decide whether to chew the raw leaf or brew an infusion? It is truly remarkable that our forbears were able to identify useful natural medicines and pass the knowledge down to us.

It is equally remarkable that modern humans with all the advantages of science are willing to put useless and potentially dangerous plant products into their bodies based on nothing better than prescientific hearsay.

Ancient Sumerians used willow, a salicylate-rich plant that foreshadowed modern aspirin. Digitalis was used by the ancient Romans long before William Withering wrote about its use for heart failure. South American natives discovered that chinchona bark, a source of quinine, was an effective treatment for malaria. These early herbal remedies pointed the way to modern pharmaceuticals. How many other early remedies fell by the wayside? What else did the Sumerians, the Romans, and the natives use that did more harm than good? If “ancient wisdom” exists, so does “ancient stupidity.”

Plants undeniably produce lots of good stuff. Today researchers are finding useful medicines in plants that have no tradition of use. Taxol, the cancer-fighting product of Pacific yew trees, was discovered by the National Cancer Institute only by screening compounds from thousands of plants.

There is a reason pharmacology abandoned whole plant extracts in favor of isolated active ingredients. The amount of active ingredient in a plant can vary with factors like the variety, the geographic location, the weather, the season, the time of harvest, soil conditions, storage conditions, and the method of preparation. Foxglove contains a mixture of digitalis-type active ingredients but it is difficult to control the dosage. The therapeutic dose of digitalis is very close to the toxic dose. Pharmacologists succeeded in preparing a synthetic version: now the dosage can be controlled, the blood levels can be measured, and an antibody is even available to reverse the drug’s effects if needed.

“Ancient wisdom” argues that if an herbal remedy has been used for centuries, it must be both effective and safe. That’s a fallacy. Bloodletting was used for centuries but it wasn’t effective and it did more harm than good. If a serious side effect occurred in one in a thousand recipients of an herb, or even one in a hundred, no individual herbalist would be likely to detect it. If a patient died, they would be more likely to attribute the cause to other factors than to herbs that they believed were safe. Even with prescription drugs, widespread use regularly uncovers problems that were not detected with pre-marketing studies.

Arguments in favor of herbal remedies include:

• They’re natural. (So what? Strychnine is natural.)
• They’re safer than prescription drugs. (Maybe some are, some aren’t; how would you know?)
• They’re milder than prescription drugs. (That would depend on the dosage of active ingredient.)
• They’re less likely to cause side effects. (When they have been as well studied as prescription drugs, they may turn out to have just as many or more side effects. All effective drugs have side effects, and if an herbal medicine has fewer side effects it might have fewer therapeutic effects too. Formal systems for reporting adverse effects have long been in place for prescription drugs; not so for herbal remedies.)
• They’re different from prescription drugs. (Some are identical to prescription drugs, like red yeast rice which contains the same ingredient as prescription lovastatin; and some herbal products have been found contaminated with prescription drugs.)
• They’re less expensive. (True, but is a cheaper, inferior product a good bargain?)
• They’re easier to obtain. (True, you don’t have to make an appointment with a doctor; but that means you don’t get the benefit of a doctor’s knowledge.)
• The mixture of ingredients in a plant can have synergistic effects. (This is widely claimed but almost never substantiated. The other ingredients are just as likely to counteract the desired effect or to cause unwanted adverse effects.)
• For every disease, God has provided a natural remedy. (Perhaps this is a comforting thought for believers, but it is not based on any evidence and is not convincing to atheists and agnostics. And it doesn’t help us find that natural remedy.)

Even when an herbal remedy works, finding a safe and reliable source is problematic. Horror stories abound:

• Contaminants (such as heavy metals, pesticides, carcinogens, toxic herbs, and insect parts).
• Wild variation in content (from no active ingredient to many times the amount on the label).
• Mislabeled products that contain an entirely different herb.

I won’t list specific examples here; they are easy enough to find. I’ll just say that natural medicines are not regulated the way prescription drugs are, thanks to the infamous Diet Supplement and Health Education Act (DSHEA) of 1994.

When you take an herbal remedy, you are taking

1. An active ingredient that usually has not been adequately tested,
2. Other components that have not even been identified, much less tested,
3. An uncertain amount, and
4. Possible contaminants.

The term “street drugs” comes to mind: you don’t really know what you’re getting.