Making Sense of Medicinal Plant Research

August 2, 2018 Maria Noel Groves

The Science of Herbs ~

Anyone who claims that “there’s no scientific evidence to support herbal medicine” clearly hasn’t been paying attention. Scientists have conducted hundreds of thousands of scientific studies on medicinal botanicals, and this data complements our long tradition (several millennia) of using plants safely as medicine. But to the general public and budding herbalists, this research seems locked away in a world of science, out of reach to the everyday person. The truth is, anyone can access the majority of this research. Once you get over a bit of a learning curve, you’ll better develop your understanding of healing plants and boost your science savvy.

Most of the scientific research you hear about in mainstream media comes through a filter. Some outlets are impartial, others incredibly biased, with the goal of either boosting herbal product sales or convincing you that herbs offer no value. By assessing the studies for yourself, you can break free of biased hype and draw your own conclusions. You just need to know where to look and how to interpret the data. First, let’s look at the different types of studies that exist and which ones provide the most useful information.

Rigorous Research

Since the 17th century, the scientific method has served as the standard for medicine. In contrast to anecdotal or experience-based medicine, this evidence-based approach is founded on the results of scientific studies. There are many ways to conduct studies, but the gold standard is the randomized, double-blind, placebo-controlled clinical (RDBPC) trial. We’ll get into more specifics, but in a nutshell, this type of trial tests two or more groups of people with and without the herb, removes most potential confounding variables (outside influences that can affect the out- come), and assesses if an herb can provide any benefit, and if so, how much. This can really shed light on which herbs show potential in treating/alleviating a given health concern, and it helps determine whether an herb really does (or does not) provide the benefit (or harm) in question.

Unfortunately, studies are myopic in nature. They look only at a specific dose of a specific extract in a specific disease measured by specific parameters, and participants are viewed as a broad group, rather than as individuals. As a result, studies rarely shed light into all the various benefits or disadvantages of a particular herb or which type of person or situation might do best with this particular medicine.

The art of herbal medicine helps match the right herbs with the individual, taking into consideration his or her whole health history, symptoms, energetics, and constitution—something science alone really can’t evaluate very well. So, while scientific studies aren’t the end-all-be-all for practicing herbal medicine, they do serve as a very useful tool for learning about and understanding herbs.

Understanding Different Types of Research

While the RDBPC study is the most reliable type of study, only a fraction of the research being conducted falls into this category because it’s time consuming and expensive. I rely on human and review studies first, and turn to animal and lab studies only when more rigorous studies aren’t available.

Human Studies

Often called in vivo or “in life” studies, these involve human participants and therefore provide the most useful, applicable information on herbs. But even these have various levels of evidence or quality, as explained below.

  1. Randomized Double-Blind Placebo-Controlled Clinical Trials (most rigorous): The RDBPC study aims to prove efficacy, cause, and effect. These studies take two or more groups of people—at the minimum, one group that receives herbs and one that receives a placebo. They may also include a third group that’s given no intervention (the term used to describe the preventative or therapeutic measure being tested; i.e., the herb), a group given standard care/pharmaceutical drugs, and/or those given the drug plus the herb.

    ensures the groups are similar in their composition for things like gender, race, age, health habits, level of disease, and biomarkers of disease. (If one group has, say, an average of 60 an- gina attacks per month and the other experiences just 10, you’re not really going to know if the herb made a difference.)

    ensures that both the study subjects and the researchers/doctors don’t know who’s receiving the real treatment or the “fake” placebo treatment. That’s to avoid placebo effect, in which participants believe they feel better or that a “treatment” is working based on their own expectations. Even the way a practitioner interacts with the client can influence perceptions and have a dramatic effect on outcome.

    makes certain that the herb is not acting as a placebo. These tests are even more accurate if they’re conducted on large groups with hundreds or thousands of people rather than a small pilot study of, say, 10 to 30 people.

    Of course, you also have to examine the study itself. Did the re- searchers use a good quality product? What was the dose, frequency, and duration? What markers were they testing?

  2. Clinical Trials (less rigorous): These studies may be very small in size and/or not include a control group. While they’re interesting and useful, they’re not as scientifically valid or reliable as RDBPC studies. You also need to be wary of bias in any study, but particularly with these, because they’re more apt to be driven by a company selling the product.
  3. Epidemiological Studies: These “population” studies are popular for nutrition and, occasionally , herbs. They look at population habits in a non-scientific setting and don’t actually prove a cause and effect but only a correlation. But they’re easier and less expensive to conduct and can tell us what to follow up on with controlled clinical trials. For example, a study might survey Japanese people to tally data on green tea consumption and cognitive decline, with results that suggest (but do not prove) that drinking two cups or more daily correlates with a 50 percent decrease in dementia symptoms.

Animal & Lab Studies

These studies are far cheaper to run than human studies, with more rapid results. But the quality of the data tends to be poor because animals and lab tests don’t necessarily correlate to human doses and the way we metabolize substances when we consume them. Taking two capsules of ashwagandha daily in a human body is much different than administering some of the herb in rat feed or exposing the herb to cancer in a petri dish.

  1. Animal Tests are often inhumane (for example, forcing rats to swim until they drown to assess adaptogenic activity), and researchers sometimes need to kill them in order to perform a necropsy (animal autopsy) at the conclusion of the study. Aside from compassion and ethical concerns, a major problem with animal studies is that they usually use much higher doses of herbs per kilo- gram of body weight than a human would typically consume. I generally ignore animal studies in favor of human studies, unless there really aren’t human studies available. Even still, always take the data of an animal study with a huge grain of salt.
  2. Lab Studies can be conducted in a test tube, petri dish, or with human or animal tissue models. They’re usually the least applicable to real life; however, they help drive future research and shed light on the mechanism(s) of an herb’s action. For example, scientists might run some lab studies on the cancer- killing abilities of popular anti- cancer herbs used by an indigenous population to determine the one or two that have the best outcomes, and then pursue these plants with more rigorous study designs. Or scientists may show that, at least in a test tube or model, an herb re- duces inflammation via a particular pathway or chemical compound.

Review studies

This kind of study assesses and consolidates the data from a variety of studies to help reach a general consensus. They often provide the most useful data—especially since studies often conflict—and are usually easier to read and understand. Review studies can compile any type of study. The best review clinical trials, particularly RDBPC, compare the statistics in a “meta-analysis,” and may even report on bias in the research. Other review studies may provide a general overview of all the research present, including lab, animal, and less rigorous human studies, as well as some historical and traditional data.

Reading Scientific Studies

Don’t take a media soundbite at face value; they often spin the data to sound better or worse (depending on whether the outlet is pro- or anti-herbs). For instance, that hot new “arthritis” herb might not have actually reduced pain and symptoms at all, but only reduced a blood biomarker of inflammation. Or the urgent warning that St. John’s wort can cause phototoxic sun rash fails to mention that this data is based on the skin reactions of albino cows, who consumed the herb while grazing in the sun all day. Learning how to track down studies and getting used to the lingo puts the power in your hands.
For those unfamiliar with scientific literature, it can sound like ancient Greek. Don’t panic. First, focus on human clinical trials and review studies, which will be easier to understand (and more applicable and valid) than animal and lab studies. Then, tease out the basics:

1. What herb(s) did they use, and in what form and dose? Did they include a placebo or control group or did they compare it to a drug? (I love drug-herb studies. They show better results more often than herb-placebo studies.)

2. How long was the study?

3. What parameters did they test (i.e., blood results, client re- ports, or questionnaire results)?

4. What were the results? How did the herb compare to placebo or control group, if available? How much of an improvement (if available) was there?

Sometimes you need to look at charts in the full text to get a better understand- ing of results. A “significant” result might mean a mere 15 percent decrease in depression symptoms or weight loss that amounts to only two pounds over six months. That might be scientifically significant, but it’s hardly impressive.

Google can serve as an ally if you’re not sure what a specific scientific term means. Also note that the oft-reported “P-Value” in scientific results summaries has more to do with how replicable those results are rather than how impressive they are.

Where to Find Scientific Studies & Scientific Data

Find the Actual Studies

PubMed, maintained by the United States National Library of Medicine (NLM) at the National Institutes of Health, remains my favorite free, search- able database for scientific studies (mostly providing abstract summaries but occasionally offering links to free full-text versions). Play around with keywords, including common and Latin plant names and different words surrounding a health concern (e.g., “inflammation,” “pain,” “arthritis,” “osteoarthritis”). Once your search results come up, click “Clinical Trial,” “Review,” and/or “Human” to narrow it down and weed out less useful studies.

Google Scholar comes in handy when PubMed doesn’t get many hits. Plug in the study name to search for full studies, too (they appear in the right column).

Sci-Hub grants access to full studies that you would otherwise need to pay for. This is moderately illegal. Because the companies that sell scientific studies and journals are constantly suing Sci-Hub, the exact website is always changing. Usually Wikipedia will show the most current access link. To use Sci-Hub, enter the DOI or PMID (which you can get on PubMed at the bottom of the abstract) into the search bar. Often, it will pull up the full-text study.

Read Study Reviews and Summaries

Other useful sites summarize evidence-based research (ideally with annotated study references so you can go back to the original studies if you so choose for more data). They’re usually easier to read than the actual studies and can help you find the right keywords. My favorites include:

  1. American Botanical Council (some items require member access)
  2. HealthNotes/Aisle7
  3. A.D.A.M.

For more details on these sites and several other useful sources, see this section of my links page. You’ll also find additional evidence-based and scientific resources listed there.

A Word on Anecdotal or “Experience-Based” Information

People have been using herbal medicine quite successfully in a wide range of health conditions for millennia. This knowledge is based on direct observation of how plants affect people and disease, as well as the wisdom passed down from mentor to student and writer to reader. Scientists call this type of information “anecdotal” because it usually hasn’t been subjected to rigorous scientific testing methods. With so many variables, only a handful of cases, and issues surrounding placebo effect, it’s difficult to be 100-percent sure the herb will reliably do what you think it does for most people. That said, experience-based information tends to be more detailed, nuanced, and useful in our day-to-day life, forming a fuller picture of a plant and how it’s best used. Many things simply haven’t been studied. You’ll get this from classes, herb books and articles written by actual herbalists who use the plants for themselves and in their practices. In truth, I find this tends to be useful for everyday people and the budding herbalist, but I like to pair it with scientific evidence.


Maria Noël Groves, RH (AHG), is a registered clinical herbalist nestled in the pine forests of New Hampshire. She is the best-selling author of Body into Balance: An Herbal Guide to Holistic Self Care, and her second book on medicinal herb gardening, Grow Your Own Herbal Remedies, releases in 2019.

This article was originally published in Herb Quarterly magazine.