Herbal Medicines: Can Herbs Cure Diseases?

Herbal Medicines: Can Herbs Cure Diseases?

Pain, high blood pressure and allergy can be treated with plant substances. Researchers are looking for new drugs in nature - but in their eagerness to find active substances, they can forget a scientific rule - missing effect is also a significant result.

Plants produce numerous chemical compounds that, among other things, protect them against insects and other pests. Many of the substances also affect humans and with some small chemical changes they can be converted into effective drugs.

Science makes its verdict: Plants relieve depression

The content of active substances in leaves, fruits and roots is low, which is one of several reasons why it can be challenging to demonstrate an apparent effect of the treatment in scientific experiments. St. John's wort is one of the plants that has a well-documented effect on the brain by affecting so-called neurotransmitters and thus counteracting depression.

Well substantiated effect

    • Depression: Genuine St. John's wort
    • Irritable bowel: Peppermint
    • Respiratory tract infections: Pelargonia

Likely effect

    • Anxiety: Kava plant
    • Arthritis: Stone rose

Lack of good evidence

    • Asthma and allergy: Pestilence
    • Nausea: Ginger
    • Heart failure: Trubhag tower
    • Poor blood circulation: Horse chestnut

Probably no effect

    • Memory loss: Ginkgo
    • Elevated cholesterol: Garlic
    • Cold: Echinacea



According to WHO, 4 billion people - 80 percent of the world's population - use herbal medicine. In developing countries, herbs are often the primary drugs.

64% of all new drugs approved between 1981 and 2010 originated in plants, fungi, animals or microorganisms.

A fog cloud of fungal spores blows across the ground full of buttery yellow St. John’s wort and descends over the small leaves.

Soon the spores begin to grow between the leaves’ cells so that they wither within a few days. But the blades have a secret weapon.

In small glands, they hide the chemical warfare agent hypericin, which tears the cell walls of the fungus and kills the uninvited guest.

As soon as the plant registers the infection, it increases production – which farmers are happy with.

The chemical weapon has an entirely different function in humans. The dried leaves have a well-documented antidepressant effect and are sold at pharmacies and in health food stores.

What is Herbal Medicine?

Herbal remedies are parts or extracts of plants – leaves, roots, flowers, bark and fruit – used to treat or prevent diseases. The use of herbal medicine is rarely based on knowledge of the various medicinal products, but rather on anecdotal experiences.

St. John’s wort is not a special case. Scientists have isolated hundreds of chemical compounds that plants use to protect themselves.

Many of them have apparent medical effects, while the effects of many others are mediated exclusively through oral tradition. This makes the market for herbal medicine difficult to navigate – especially considering that the scientific studies do not necessarily provide clarity on what is fact or fiction.

In some cases, researchers see experimental results that do not show any beneficial effect on the herbs as uninteresting and therefore allow them to end up in the desk drawer in the form of self-censorship. It is a dangerous pitfall that can give a false impression that herbal medicine works better than it actually does.

Plants became Socrates dead

The use of herbs as a medicine goes back thousands of years. Long before the founding of modern medical science, people have noticed that the leaves, fruits and roots of plants can affect the body in different ways.

A large number of plants have long been used, for example, for their toxic properties. When tribal people in the Amazon rainforest went hunting, their arrowheads were poisoned with curare, which is an extract of bark from the veal plant. And when the death sentence on Greek philosopher Socrates was executed some 2,400 years ago, he was forced to drink herbal juice with a deadly amount of poisonous alkaloids.

Many plants proved to have a beneficial effect and doctors in the past discovered the bark, which at that time was prescribed in the form of tea against both pain, fever and inflammation.

At the end of the 19th century, a German chemist concluded that its beneficial effect was due to the bark’s content of salicylic acid. With the help of a simple chemical change, the pharmaceutical company Bayer converted the natural substance into acetylsalicylic acid, which today is part of well-known drugs such as aspirin and treo.

Similarly, ancient “wise gums” used dried leaves of the plant thimbles to treat heart disease. This was a long time before researchers found out that the plant contains the substance digitalis, which causes the heart to beat more slowly and with greater strength.

In the same way, many other drugs of today’s medicine originate in nature.

Often, scientists do not know for sure which substances in the plant have the medicinal effect. This applies, for example, to St. John’s wort. Until a couple of years ago, researchers considered that it was only the topic of hypericin.

New research suggests that other substances in the plant, including hyperforin, also help to affect the amount of so-called neurotransmitters in the brain and thus contribute to the antidepressant effect.

In 2009, in a comprehensive analysis of several scientific studies, a so-called meta-analysis, researchers came to three conclusions about the plant’s effect on depression: Genuine St. John’s wort works significantly better than a placebo in treating depression, the plant is as effective as regular antidepressants. Also, it has comparatively fewer side effects.

The analysis was carried out by the German physician Klaus Linde from the Munich University of Technology. It was a comprehensive review of a total of 29 studies that other researchers had conducted on more than 5,000 subjects.

In 2016, researchers in a similar meta-analysis with 7,000 subjects reached the same three conclusions, giving the plant a place on the list of herbs that have a documented effect on serious diseases. Other

well-documented variants of herbal medicine are, for example, peppermint against irritable colon and geranium against respiratory tract infection.

Roots can affect memory

Health food stores, supermarkets and pharmacies also sell many herbs with more questionable underpinnings. Scientific experiments cannot support the effect of the popular Echinacea garden plant on colds.

In a meta-analysis from 2014, the researcher compared Marlies Karsch-Völk from the Technical University of Munich in Germany, the results of 24 studies conducted by other researchers, with a total of 4,631 subjects.

The analysis concluded that preventative treatment with Echinacea in the form of either dried plant parts, juice or extracts from the roots only reduced the risk of being chilled by ten percent.

And if Karsch-Völk included the statistical uncertainty in the calculation, the effect was doubtful. Neither does the plant’s ginseng’s highly-prized ability to enhance all of the brain’s mental processes, the so-called cognitive function, is particularly convincing in scientific experiments.

In a 2010 study involving nine studies, researcher Jian-Cheng Dong, from the Nantong University Medical School of China, concluded that a daily dose of between 200 and 400 milligrams of ginseng extract provided a small but statistically significant improvement in short-term memory and responsiveness.

However, the researchers measured no effect on concentration or brain counting capacity. Jian-Cheng Dong drew the conclusion that ginseng is likely to improve some aspects of brain function, but that there are too few studies to reach a definitive conclusion.

Missing tests

A general problem with herbal medicines is that the products are rarely particularly well tested. Chemist Giancarlo Cravotto from the University of Turin, Italy, showed in 2010 that twelve percent of the most widely used herbal medicines in the western world have not been tested in any scientific studies. We know nothing about which substances the herbal medicine contains, whether it is safe to consume or whether it has any beneficial effect on health.

One-fifth of the popular herbal medicines have undergone chemical analyzes, so we at least know if they contain substances of known effect, and half have been tested on animals to investigate if the drug is toxic or has serious side effects. But only 16 percent have been tested in clinical trials in humans.

The lack of documentation is also well known by US health authorities that have a special national center for alternative medicine, NCCIH.

On their website, they list 52 herbs that are often used as a remedy for various ailments. In 44 of them, NCCIH has found that either no research has been conducted on them, or that the research is poor quality that there is no evidence of their effect.

In some cases, therefore, consumers live in complete uncertainty as they try to relieve their symptoms with herbal medicine.

Although the preparation has been tested in clinical trials in humans, it does not necessarily mean that it has any established effect. One of the most widely used and tested forms of herbal medicine is cranberry juice used to treat and prevent urinary tract infection.

But according to a 2013 meta-analysis, the effect of the red drink is mostly a myth.

Chills the will of the subjects

Researcher Ruth Jepson from Scotland’s equivalent to the National Board of Health compared results from 24 studies with a total of 4,473 subjects and concluded that the preventive effect of cranberry juice was minimal and not statistically significant. She also noted that many of the studies had a considerable dropout of subjects – as much as 55 percent in one study because they did not manage to drink a large glass of cranberry juice a day.

The treatment requires a certain will from the patient and may not be suitable for those who prefer simple solutions. This also applies to other types of herbal medicines, for example, it can be difficult to prepare a daily ginger threat or to eat garlic, whose scent can trouble others.

But if the researchers do not include it in their overall conclusions, the significant dropout is also a problem purely scientific. For example, if the sickest patients are cranberries and instead take antibiotics to recover quickly, only the least ill will remain in the study.

Of course, they become more easily healthy – which increases the risk of the red liquid appearing to be more effective than it actually is.

Sunshine stories are doubtful

Another form of distortion in the studies of herbal medicine occurs if the success stories are to be completely contradicted. This applies not only in regular communication between people, but also to a large extent in scientific literature, as many researchers choose not to publish any negative results – partly because it can be perceived as unsuccessful and partly because it can simply be uninteresting for the researchers themselves.

The phenomenon is called the box office effect or publication bias and is well known in all kinds of clinical trials, but especially in herbal medicine studies. The distortion is often expressed in connection with the so-called meta-analyses, where the researchers behind the analyzes prefer to include studies with positive results in their overall conclusion.

Ken Naumann works as a biologist at Langara College in Vancouver, Canada, in 2018 published an accurate rendition of the credibility of scientific studies of herbal medicine.

A review of 160 meta-analyses published between 2010 and 2014 showed that no less than 90 percent of the analyses based their conclusions on questionable grounds, as they placed greater emphasis on studies that led to a positive result regarding the effect of the herbs. Thus, distortion is one of the significant credibility problems of herbal medicine.

In other words, science does not support a decision to replace the pill cans with roots, leaves and extracts. However, most scientists agree that the herbs generally have fewer side effects than regular drugs, since the plants usually contain lower concentrations of several active substances – while the doctor’s pills typically contain a single active substance in high concentration.

The herbs thus have their advantages – in cases where their effect is actually well documented.

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