Mycotoxins in Medicinal Herbs: An Under-Appreciated Risk?

Fungal organisms are a normal part of the microbiome of plants. Some of these fungal organisms produce secondary metabolites which are toxic to animals and people. Some mycotoxins are potent carcinogens [1]. Much of the research on these and the risk to health posed by them has been done on commercial crop vegetables. There is current concern about the potentially increasing risk of aflatoxin in US maize due to climate change [2]. Also under the microscope, so to speak, are organic crops because they are not subject to the same mycotoxin control measures as non-organic crops [3].

But mycotoxin contamination of herbal products also represents a possible risk for human health. One study, the aim of which was to assess the extent of this problem, analysed a variety of herbal-based supplements from Czech and US markets – including milk thistle, red clover, flax seed, soy, green barley, nettle, goji berries and yucca – for the presence of 57 mycotoxins. Mycotoxin contamination was found to be more prevalent than expected, with 96% of the 69 herbal supplement samples containing detectable mycotoxins. The highest mycotoxin concentrations were found in milk thistle-based supplements (up to 37 mg/kg). [4]

Milk thistle (Silybum marianum L.) seed head. Public domain image from

Caldeirao et al. (2021) carried out a study of fourteen mycotoxins in a range of herbs in the Brazilian market, as dried herbs and infusions. They found mycotoxin contamination in 42 out of 58 herb samples (72%). In herbal infusions however, the occurrence of mycotoxins was 88% lesser than those in raw products. But despite this, the authors assessed that in the case of HT-2 toxin and in the case of some herbal infusions also aflatoxins and ochratoxin A, the levels found in infusions posed potential health risks. [5]

Hassan et al. (2022) evaluated the prevalence of aflatoxin B1 (AFB1) and ochratoxin A (OTA) in thyme and thyme-based products, related dietary exposure, and cancer risk for regular and high consumption. From the abstract:

A total of 160 samples were collected, and 32 composite samples were analyzed. AFB1 and OTA were respectively found in 84% … and 38% … of the samples. AFB1 exceeded the limits in 41% … and 25% … of the samples according to the Lebanese and European standards, respectively. OTA was unacceptable in only 6% … and 3% … of the samples according to the Lebanese and European standards, respectively.

After estimating daily exposure levels for Lebanese consumers on the basis of a food-frequency questionnaire, the authors calculate that the AFB1 exposure from dried thyme as a herb would account for 0.41 additional cancer cases per 100,000 persons, and from thyme-based products 0.35 additional cases per 100,000. [6]

However, a Latvian study concluded that while 90% of dry herb samples were contaminated with 1-8 mycotoxins, and despite high levels of extraction into infusion for some of them, intake risk assessment indicated that the tested herbal infusions were safe for consumers. [7]

And in a study of seven mycotoxins in supplements made with fifteen different single herbs and two compound supplements for two kinds of complaints, Pallarés et al. (2022) found that, although mycotoxin contamination was quite prevalent (58.3% of organic versus 41.1% of conventional samples) estimated daily intakes for mycotoxins, calculated according to the supplement manufacturers’ recommended dosages, were in general far below Tolerable Daily Intakes (TDIs). [8]

Moreover, Do et al. (2015) point out that exposure and toxicities can be diversely influenced by the other constituents of medicinal plants. They comment:

Although the occurrence and exposure of mycotoxins in most medicinal herbs and spices in various countries are inevitable, many of the bioactive components in these agricultural commodities have been known to regulate the fungal growth, mycotoxin production and their toxic actions in the plant and its herbivores, including human beings and domestic animals. These endogenous components are thus crucial attenuators by reducing the inevitable exposure and toxicities when taken in together with the contaminated mycotoxins.

Nevertheless, they also warn that:

… since some natural endogenous components could enhance the toxicity of mycotoxins via metabolic activation or retarded secretion by complex formation with mycotoxins, extensive investigations into these interactions is warranted. [9]

Pallarés et al. (2022), despite their encoraging findings (see above), also warn that:

The rising market of herbal products in Europe and worldwide makes necessary the control of mycotoxins and other chemical contaminates in such products. Poor practices during harvesting, handling, storage, and distribution stages affect the quality and safety of medicinal herbs, so the implementation of good manu-
facturing practices is essential to reduce mycotoxins presence.
[My highlighting] [8].

Aspergillus flavus Link. Photo by Swathi Sridharan via Flickr. CC BY-SA 2.0 licence.

This brief post cannot pretend to be anything approaching a comprehensive review of this subject. It simply aims to sample a few recent papers in order to alert the herbal community to what may be a lesser known or under recognised issue.

Yu et al. (2021) have provided a review [10], the abstract of which reads as follows:

Herbal medicines have been applied in clinical treatment worldwide, whose significant curative effect attracts considerable global research attention. However, as the herbal medicine industry
develops continuously in recent years, new challenges including monitoring the quality and safety of herbal medicines appear in this industry. Numerous cases of fungal and mycotoxin contamination have been reported that affected the quality and safety of herbal medicines. The main mycotoxins found in herbal medicines include aflatoxin, ochratoxin A, and fumonisin B, which cause substantial harm to human health. They are mainly produced by species from Aspergillus, Penicillium, and Fusarium. Various reports have focused on studying the conditions for fungal growth and mycotoxin synthesis to provide references for prevention. The chemical compounds and antagonism microorganisms were also explored to inhibit fungal growth, and decrease mycotoxin accumulation. This review discusses natural occurrence of three main fungal genera (Aspergillus, Penicillium, and Fusarium) and three main mycotoxins (aflatoxin, ochratoxin A, and fumonisin B) in herbal medicines, analyzing the endogenous and exogenous factors that affect fungal growth and mycotoxin production. Moreover, the prevention methods of fungal contamination are included.

Important questions remain for the small scale herbalist wildcrafting or growing herbs to make medicines for family and friends. Laboratory testing is expensive and may not be locally available. It is clearly impossible to remove all possibility that mycotoxins will be present in their herbal preparations. So what steps can be taken to minimise the risk? At the present time I can offer only the following:

  • Inspect all fresh herbs closely for any signs of mould, disease or or less than perfect quality.
  • Use them fresh or process them immediately.
  • If drying the herbs, make sure they are fully dried.
  • Store in airtight jars in a cool, dry space out of direct sunlight.
  • Inspect regularly for signs of deterioration.
  • Use dried herbs within two years.
  • When making ethanolic tinctures make sure the ethanol content is sufficient to prevent microbial growth.
  • Make sure herb material is completely covered by the menstruum.
  • Allow as little air space in the jar as possible.
  • Shake well regularly.
  • Strain at no more than 6 weeks.


[1] Wikipedia. Mycotoxin. N.d. Accessed 11th July 2022.

[2] Bailee Henderson. The Future of Aflatoxin in U.S. Corn. 23rd June 2020. Food safety Magazine. Accessed 11th July 2022.

[3] Wageningen University and Research. EU project Safe Organic Vegetables. N.d. Accessed 11th July 2022.

[4] Veprikova Z, Zachariasova M, Dzuman Z et al. Mycotoxins in Plant-Based Dietary Supplements: Hidden Health Risk for Consumers. 2015. J. Agric. Food Chem. 2015; 63(29):6633–6643. Abstract:

[5] Caldeirão L, Sousa J, Nunes LCG et al. Herbs and herbal infusions: Determination of natural contaminants (mycotoxins and trace elements) and evaluation of their exposure,
Food Research International. 2021; 144(110322).

[6] Hassan HF, Koaik L, Khoury AE et al. Dietary Exposure and Risk Assessment of Mycotoxins in Thyme and Thyme-Based Products Marketed in Lebanon. Toxins. 2022; 14(5):331.

[7] Reinholds I, Bogdanova E, Pugajeva I, Bartkevics V. Mycotoxins in herbal teas marketed in Latvia and dietary exposure assessment. Food Additives & Contaminants: Part B. 2019; 12(3):199-208. DOI: 10.1080/19393210.2019.1597927

[8] Pallarés N, Berrada H, Font G, Ferrer E. Mycotoxins occurrence in medicinal herbs dietary supplements and exposure assessment. 2022. J Food Sci Technol. 2022; 59(7):2830–2841.

[9] Do KH, An TJ, Oh S-K, Moon Y. Nation-Based Occurrence and Endogenous Biological Reduction of Mycotoxins in Medicinal Herbs and Spices. Toxins. 2015; 7(10):4111-4130.

[10] Yu J, Yang M, Han J, Pang X. Fungal and mycotoxin occurrence, affecting factors, and prevention in herbal medicines: a review. Toxin Reviews. 2021. DOI: 10.1080/15569543.2021.1925696

Copyright (c) Robert Hale 2022.

Intelligent Plants?

A Sensitive Plant in a garden grew,
And the young winds fed it with silver dew,
And it opened its fan-like leaves to the light.
And closed them beneath the kisses of Night.

The Sensitive Plant, a watercolour by Frank Bernard Dicksee (1853-1928) depicting Percy Bysshe Shelley’s poem (see above). Public domain, via Wikimedia Commons.

The publication of a recent paper (Khattar et al., 2022) [1] examining acceptance among scientists of various disciplines of the concept of plant intelligence provoked online enthusiasm among some herbalists, in terms such as:

“It hearkens to an emerging, emboldened approach to scientific investigation that finally dispenses with monotheism-informed, limiting belief structures and subtexts, allowing for the contemplation of intelligence and consciousness in non-human beings… (such as) …plants and dissimilar creatures in particular.”

The paper’s authors acknowledge that semantics is an issue and provide the following definition of plant intelligence:

Any type of intentional and flexible behavior that is beneficial and enables the organism to achieve its goal.”

They give some examples of behaviours which might be viewed as evidence of plant intelligence:

“the ability to problem-solve in a flexible manner, anticipate the future, store memory, learn, communicate, and ultimately be goal-oriented.”

Specific examples include:

  • Volatile chemicals being produced at the appropriate time, concentration, and amount as defence against herbivores.
  • The above behavioral responses affecting, and being affected by, neighboring plants, shaping plant communities.
  • The capability to custom-modify the quality and quantity of their nectar to attract the right species of ants to protect them, a capability that requires plants to sense the presence of different ants, and to monitor and modify their own activity accordingly.
  • The ability to anticipate the future as demonstrated, for example, in the way plants rely on light cues to remember the exact number of warm days or daylight hours (i.e., photoperiodic control) that have passed to develop their leaves and flower.
  • The ability to learn to make new associations through multiple cues and to respond adaptively. Conditioned learning of this type has been demonstrated in the pea plant (Pisum sativum L.).
  • Various types of foraging behavior for sunlight and nutrients exemplify how plants can be goal-oriented. Example: the ability of the pea plant to modify root-growth in response to varying nutrient concentrations.
  • The capability to manipulate herbivores to adopt cannabalistic behaviour by releasing certain chemicals, as demonstrated by some tomato plants (Solanum lycopersicum L.).

These capabilities are indeed fascinating, but do they demonstrate intelligence? This clearly hinges upon our definition of intelligence, and according to the study author’s definition, I would judge that they do not. The problem is with the word “intentional”. I would agree that to be “goal-oriented” is not enough for a behaviour to demonstrate intelligence, it must be intentional. And does not intention imply consciousness? None of the behaviours described above demonstrates consciousness. It may be there at some level (if not individual then within the community), but it has not been shown to be there.

But I am more interested in a further facet of this debate. Just say that we all agreed that plants possess some form of intelligent consciousness (remember, intention requires consciousness), would that be be anything like ours, something we as human beings could relate to? Because this is what some herbalists fancy. That plants can talk to us and we can understand them; even that they may feel well-disposed towards us.

I have little doubt it would not. I know quite a lot at an experiential level about fish, which are more closely related to us than are plants. I swim with them often and sometimes I catch them to eat. Some species are curious about people, most are not, and some will swim away very fast at the first sight of a human being. I like them. But they cannot “like” me, even the curious ones, they are merely curious in some kind of fishy way. Why on Earth should intelligent fish like human beings? If I were an intelligent fish I would have a great big prejudice against them, wouldn’t you? But fish are most probably incapable of emotion. Their behaviour is goal-oriented (even intentional) and flexible, but whatever form their “thoughts” take, they are nothing like mine. I can hardly conceive of what it is like to think like a fish. Tell me, what part of the above reasoning cannot be applied to plants?

For some herbalists there is the romantic temptation to anthropomorphise plants or to project their own thoughts and feelings onto them, but beware! Subjective realities, while valid in some terms and for some purposes, often boil down to simple flights of fancy.

[1] Khattar, J., Calvo, P., Vandebroek, I. et al. Understanding interdisciplinary perspectives of plant intelligence: Is it a matter of science, language, or subjectivity?. J Ethnobiology Ethnomedicine 18, 41 (2022).

The Common Nettle (Urtica dioica) in Eastern Herbalism

In a previous post I presented a graphic about the Common Nettle (Urtica dioica) in Western Herbalism. This post complements that one, and deals with the use of the herb in Traditional Chinese Medicine (TCM) and Ayurveda.

If the image is too small for you to read the words, enlarge your window by holding down ‘Control’ and scrolling up with your mouse wheel.

Copyright © Robert Hale 2021.

Retrieved 19/05/2021.

2. Holmes P. (1993). The Energetics of Western Herbs, Vol. 1, Revised Second Edition. Berkeley, USA: NatTrop Publishing.

Retrieved 19/05/2021.

The Common Nettle (Urtica dioica) in Western Herbalism

If the image is too small for you to read the words, enlarge your window by holding down ‘Control’ and scrolling up with your mouse wheel.

I may cover the Ayurvedic and Traditional Chinese Medicine perspectives on Common Nettle in another post.

Copyright © Robert Hale 2021.


1. Retrieved    
2. Retrieved 23/04/21.
3. Retrieved 23/04/21.
Retrieved 23/04/21
Retrieved 23/04/21.
6. Bone S., Mills K. (2013). Principles and Practice of Phytotherapy, 2nd ed. Edinburgh (UK): Churchill Livingstone Elsevier.
Retrieved 28/04/2021.
Retrieved 28/04/2021.
9. Holmes P. (1993). The Energetics of Western Herbs, Vol. 1, Revised Second Edition. Berkeley, USA: NatTrop Publishing.
Retrieved 28/04/2021.
11. Hale R. D. (2021). My own “cheatsheet” summary.
12. Wood M. (2008). The Earthwise Herbal: A Complete Guide to Old World Medicinal Plants. (Berkeley (USA): North Atlantic Books.

Why Are Dosing Recommendations So Inconsistent in Herbal Medicine?

Photo of licorice root from Royalty-free image.

The good news is that dosing for dried herbs taken as such (for example by chewing or as a powder in a capsule or stirred into water), or in simple water-based preparations such as infusions and decoctions, are often remarkably consistent even across cultures (e.g. traditional Chinese and traditional Western).

The perplexing thing is that with other kinds of preparations, notably tinctures and other liquid extracts, dosing recommendations differ widely between authors and between schools of thought. And yet you will not meet a practitioner who does not claim good results.

What is happening here? Here are some possibilities which we ought to consider:

  1. Many plants have a very wide therapeutic window.
  2. Herbs work in different ways when prescribed at higher, lower or minute doses, however they work to the same end. For example, some practitioners believe that in small doses herbs nudge the body towards a healing response rather than taking over parts of its physiology, which happens with larger doses: the difference between a subtle suggestion and a command. Others believe that it is some “subtle energy” conveyed by the herb, rather than the chemicals it contains, that interacts with the body’s “energy” to produce a healing response. This, they say, explains its effectiveness when used in extremely tiny doses.
  3. Practitioners’ perceptions and beliefs are subject to considerable biases and therefore are not reliable reflections of reality. The reality might be that in many cases the patient’s encounter with them and the associated treatment did not materially affect the course of the patient’s condition.
  4. The patient’s encounter with them and the associated treatment did affect the course of the patient’s condition, but this was not due in any way to the kind of herb prescribed, its dose or the nature of its preparation. It was due to other factors in the context of the interaction which we shall call “non-specific factors” e.g. the patient liked the practitioner and perceived them to be trustworthy and competent, which engendered belief in the treatment prescribed.
  5. More than one of these things are happening at the same time.

Number 5 is my best guess, with the proviso that with regard to number 2, I do not believe in “subtle energies” disembodied from the chemistry of life. But I would like to direct people’s attention to numbers 3 and 4, the importance of which I believe most practitioners vastly underestimate, and some even deny. As practitioners of a non-conventional system of medicine, there is a tendency to be defensive on these matters, which is understandable as it is a commonplace for sceptics to assume, “Well, it’s all placebo, isn’t it?” But non-specific effects along with patient and practitioner biases and are normal phenomena occurring every day in all branches of medicine, conventional and non-conventional, all over the world. Only if we admit their importance and attempt to account for them can we move to a more mature understanding of our discipline and our art as practitioners.

Copyright © Robert Hale 2021.