Rhus ovata fruit by E. Yarnell
Here I will present a periodically updated list of myths in herbal medicine. There are ever so many! I hope this will serve as a tool to improve clinicians' and students' understandings of clinical use of botanical medicines. I'm sure some will latch on to these as some kind of attack on herbal medicine or some attempt to discredit it. Nothing could be further from the truth---I feel it is important to be honest that there are common errors in circulation about herbal medicine, and I want to correct them. The same is absolutely true of conventional medicine. Anyhow, enjoy.
Last updated 26 Nov 2023
Myth: Herbs Rich in Coumarin are Anticoagulant
This is a classic example of a common type of myth, in which a constituent from a medicinal plant is isolated and concentrated, and shown to have some kind of problem. Then that problem is said to occur when using the whole plant. This is absurd to say the least. In this case it is even more absurd, because the constituent in question (coumarin) isn't even what is causing the problem, but instead a semi-synthetic drug based on this constituent, which was unfortunately given the trade name Coumadin. Literally, this now seems to be a problem where people can't tell the word coumarin from the word Coumadin.
If you have access to a human clinical trial showing that any non-fermented herb containing coumarin regularly causes bleeding in people, please send it to me (because I sure can't find any such evidence). I recognize that plants containing coumarin can ferment and develop levels of anticoagulant metabolites such as dicoumarol; that's why I specified the non-fermented part.
I have written a more extensive article on this topic, which you can download here if you want to reach more details including citations to the scientific literature showing that isolated coumarin is not an anticoagulant.
If you have access to a human clinical trial showing that any non-fermented herb containing coumarin regularly causes bleeding in people, please send it to me (because I sure can't find any such evidence). I recognize that plants containing coumarin can ferment and develop levels of anticoagulant metabolites such as dicoumarol; that's why I specified the non-fermented part.
I have written a more extensive article on this topic, which you can download here if you want to reach more details including citations to the scientific literature showing that isolated coumarin is not an anticoagulant.
Myth: Ginkgo, Garlic, and Ginger are anticoagulant and antiplatelet at reasonable doses.
The vast majority of the clinical trial evidence for all three of these herbs absolutely does not support this idea. The widespread advice to avoid these herbs when having surgery or in combination with anticoagulant/antiplatelet drugs is directly contradicted by clinical trials showing now harm, and sometimes benefit, with such combinations. For each of these herbs I have a more in depth discussion of the research supporting this located elsewhere as follows:
Allium sativum (garlic) article
Ginkgo biloba (ginkgo) article
Zingiber officinale (ginger) article
Allium sativum (garlic) article
Ginkgo biloba (ginkgo) article
Zingiber officinale (ginger) article
Myth: Actaea racemosa (black cohosh) is a phytoestrogen
Some very early German rat studies suggested a phytoestrogenic effect from black cohosh extracts (Jarry and Harnischfeger 1985; Jarry, et al. 1985). These results have not been replicated in subsequent animal and human studies, but in fact repudiated (Einer-Jensen, et al. 1996; Wuttke, et al. 2014). This is not to say that black cohosh doesn't have clinical benefits for women with menopausal symptoms or other issues, only that its benefits are not due to a phytoestrogenic mechanism of action.
Black cohosh does contain the phytoestrogenic compound formononetin, but at levels far too low to possibly be relevant clinically (Panossian, et al. 2004; Kennelly, et al. 2002).
References
Einer-Jensen N, Zhao J, Anderson KP, Kristofferson K (1996) "Cimicifuga and Melbrosia lack estrogenic effects in mice and rats" Maturitas 25(2):149–53.
Jarry H, Harnischfeger O (1985) "Endocrine effects of constituents of Cimicifuga racemosa. 1. The effect on serum levels of pituitary hormones in ovariectomized rats" Planta Med 51:46–9 [in German]
Jarry H, Harnischfeger O, Düker E (1985) "The endocrine effects of constituents of Cimicifuga racemosa. 2. In vitro binding of constituents to estrogen receptors" Planta Med (4):316–9 [in German]
Kennelly EJ, Baggett S, Nuntanakorn P, Ososki AL, Mori SA, Duke J, Coleton M, Kronenberg F (2002) “Analysis of thirteen populations of black cohosh for formononetin” Phytomedicine 9(5):461–7.
Panossian A. Danielyan A. Mamikonyan G. Wikman G (2004) “Methods of phytochemical standardisation of rhizoma Cimicifugae racemosae” Phytochem Anal 15(2):100–8.
Wuttke W, Jarry H, Haunschild J, et al. (2014) "The non-estrogenic alternative for the treatment of climacteric complaints: Black cohosh (Cimicifuga or Actaea racemosa)" J Steroid Biochem Mol Biol 139:302–10.
Black cohosh does contain the phytoestrogenic compound formononetin, but at levels far too low to possibly be relevant clinically (Panossian, et al. 2004; Kennelly, et al. 2002).
References
Einer-Jensen N, Zhao J, Anderson KP, Kristofferson K (1996) "Cimicifuga and Melbrosia lack estrogenic effects in mice and rats" Maturitas 25(2):149–53.
Jarry H, Harnischfeger O (1985) "Endocrine effects of constituents of Cimicifuga racemosa. 1. The effect on serum levels of pituitary hormones in ovariectomized rats" Planta Med 51:46–9 [in German]
Jarry H, Harnischfeger O, Düker E (1985) "The endocrine effects of constituents of Cimicifuga racemosa. 2. In vitro binding of constituents to estrogen receptors" Planta Med (4):316–9 [in German]
Kennelly EJ, Baggett S, Nuntanakorn P, Ososki AL, Mori SA, Duke J, Coleton M, Kronenberg F (2002) “Analysis of thirteen populations of black cohosh for formononetin” Phytomedicine 9(5):461–7.
Panossian A. Danielyan A. Mamikonyan G. Wikman G (2004) “Methods of phytochemical standardisation of rhizoma Cimicifugae racemosae” Phytochem Anal 15(2):100–8.
Wuttke W, Jarry H, Haunschild J, et al. (2014) "The non-estrogenic alternative for the treatment of climacteric complaints: Black cohosh (Cimicifuga or Actaea racemosa)" J Steroid Biochem Mol Biol 139:302–10.
Myth: Glycyrrhiza spp (licorice) causes hypertension at any dose
Yes, licorice can cause hypertension. The issue is that there are safe doses of it that will not do this, except in patients who are exquisitely sensitive.
I discuss these issues in depth in my article on why Glycyrrhiza is THE single most important herb.
I discuss these issues in depth in my article on why Glycyrrhiza is THE single most important herb.
Myth: If an herb is for sale, it must not be endangered and it must come from a sustainable source
Nothing could be further from the truth. The reality is there is a thriving trade in many endangered plants (not to mention animals). This leads to a widespread sense that if the herb is so available, how could it possibly be threatened or endangered? People also foolishly believe that every company is sourcing materials only from sustainably sources, though they almost never actually reveal their sources so how this would be known is a complete mystery (and most companies depend on people not asking uncomfortable questions about such matters). There is an understandable focus in most venues on trying to preserve endangered animal species, leading to so-called "plant blindness" when it comes to the licit and illicit trade in endangered species.
References
See the database on threatened and endangered medicinal herbs on this site.
Chen SL, Yu H, Luo HM, et al. (2016) "Conservation and sustainable use of medicinal plants: Problems, progress, and prospects" Chin Med 11:37.
De Angelis P, Timoshyna A (2020) "Strengthening sustainable international trade in medicinal and aromatic plants" HerbalGram 127:28–34.
Lavorgna A, Sajeva M (2021) "Studying illegal online trades in plants: Market characteristics, organisational and behavioural aspects, and policing challenges" Eur J Criminal Policy Res 27:451–70.
Margulies JD, Bullough LA, Hinsley A, et al. (2019) "Illegal wildlife trade and the persistence of 'plant blindness'" Plants People Planet 1(3):173–82.
Pimm SL, Russell GJ, Gittleman JL, Brooks TM (1995) "The future of biodiversity" Science 269(5222):347–50.
References
See the database on threatened and endangered medicinal herbs on this site.
Chen SL, Yu H, Luo HM, et al. (2016) "Conservation and sustainable use of medicinal plants: Problems, progress, and prospects" Chin Med 11:37.
De Angelis P, Timoshyna A (2020) "Strengthening sustainable international trade in medicinal and aromatic plants" HerbalGram 127:28–34.
Lavorgna A, Sajeva M (2021) "Studying illegal online trades in plants: Market characteristics, organisational and behavioural aspects, and policing challenges" Eur J Criminal Policy Res 27:451–70.
Margulies JD, Bullough LA, Hinsley A, et al. (2019) "Illegal wildlife trade and the persistence of 'plant blindness'" Plants People Planet 1(3):173–82.
Pimm SL, Russell GJ, Gittleman JL, Brooks TM (1995) "The future of biodiversity" Science 269(5222):347–50.
Myth: Piper methysticum (kava) is hepatotoxic.
I have detailed the case showing this herb is not hepatotoxic at my article, which you can read here.
Myth: Curcumin is clinically superior to whole Curcuma longa (turmeric) rhizome.
Using a tiny set of constituents (curcumin) from an herb with a 10,000+ year history of clinical use and efficacy is illogical. Where are the head-to-head clinical trials showing curcumin is superior to turmeric? They don't exist! The push to use curcumin instead of turmeric is based on marketing, and mostly based on pharmacokinetic arguments that don't actually tell us what we need to know as clinicians. I dissect this issue in depth in an article located here.
Myth: Capsella bursa-pastoris (shepherd's purse) stops uterine bleeding because it is astringent
This is self-evident from tasting the herbs. Tannin rich herbs have the distinctive astringent mouth feel when you put them in your mouth. This herb simply doesn't have that, but instead the more typical sulfurous taste that comes from it being a member of the Brassicaceae family and being rich in glucosinolates. Even though it may well contain significant tannins and their taste is simply covered by these other constituents, it is doubtful these are what make the herb effective in practice for reasons discussed below (Neagu 2019).
This myth is perpetuated in many herb books, and it seems to originate from an obvious misunderstanding. Many herbs that help reduce bleeding are astringent and rich in tannins. This herb's traditional use is also to stop bleeding, so I think many writers assume it must be astringent. It is just not true that an herb must be astringent to stop bleeding. This in fact doesn't really make any sense when it comes to the main use of shepherd's purse, which is to relieve excessive menstrual and postpartum bleeding. Tannins are not significantly absorbed (if they are, they are quite toxic) and there is no obvious way for them to get to the uterus to have such an effect. Many other astringent herbs that are clearly helpful for reducing uterine bleeding (Cinnamomum app, Mitchella repens, Alchemilla app, and Trillium spp leap to mind) probably actually work because of other constituents in them, but this has not really been studied so it is only a guess and logical extrapolation from the known pharmacokinetics and toxicology of tannins.
One of the few published clinical trials that supposedly documents a reduction in postpartum hemorrhage with shepherd's purse doesn't provide much clarification (Ghalandari, et al. 2017). The dose utilized in this trial was just 10 drops given sublingually, which the paper most clearly states contained 500 mg of a tincture of Capsella, though later erroneously claims it contained 5 g of the extract. Such a tiny dose is unlikely to be effective, even though it appeared to be superior to placebo at reducing bleeding. If it was truly effective, it is again very difficult to posit a mechanism whereby tannins applied under the tongue would account for the results. It is more likely other constituents were causing vasoconstriction.
Another clinical trial in women with heavy bleeding and uterine fibroids used a more reasonable dose of a high-ethanol encapsulated extract, apparently providing the equivalent of 14 g of herb a day, and determined the extract contained 4.57% tannins, which is admittedly a fairly high amount (Danesh 2019). Though this extract did reduce bleeding, it was not significantly different from the placebo control.
It is also worth noting that one of the earliest modern publications about shepherd's purse attributed its hemostatic effects to the presence of a common fungal pathogen of Brassicaceae-family plants, known now as Albugo candida = Cystopus candidus (Steinmetz 1954). No research could be identified regarding this theory, so it is unknown if it is true or itself a myth.
This myth is perpetuated in many herb books, and it seems to originate from an obvious misunderstanding. Many herbs that help reduce bleeding are astringent and rich in tannins. This herb's traditional use is also to stop bleeding, so I think many writers assume it must be astringent. It is just not true that an herb must be astringent to stop bleeding. This in fact doesn't really make any sense when it comes to the main use of shepherd's purse, which is to relieve excessive menstrual and postpartum bleeding. Tannins are not significantly absorbed (if they are, they are quite toxic) and there is no obvious way for them to get to the uterus to have such an effect. Many other astringent herbs that are clearly helpful for reducing uterine bleeding (Cinnamomum app, Mitchella repens, Alchemilla app, and Trillium spp leap to mind) probably actually work because of other constituents in them, but this has not really been studied so it is only a guess and logical extrapolation from the known pharmacokinetics and toxicology of tannins.
One of the few published clinical trials that supposedly documents a reduction in postpartum hemorrhage with shepherd's purse doesn't provide much clarification (Ghalandari, et al. 2017). The dose utilized in this trial was just 10 drops given sublingually, which the paper most clearly states contained 500 mg of a tincture of Capsella, though later erroneously claims it contained 5 g of the extract. Such a tiny dose is unlikely to be effective, even though it appeared to be superior to placebo at reducing bleeding. If it was truly effective, it is again very difficult to posit a mechanism whereby tannins applied under the tongue would account for the results. It is more likely other constituents were causing vasoconstriction.
Another clinical trial in women with heavy bleeding and uterine fibroids used a more reasonable dose of a high-ethanol encapsulated extract, apparently providing the equivalent of 14 g of herb a day, and determined the extract contained 4.57% tannins, which is admittedly a fairly high amount (Danesh 2019). Though this extract did reduce bleeding, it was not significantly different from the placebo control.
It is also worth noting that one of the earliest modern publications about shepherd's purse attributed its hemostatic effects to the presence of a common fungal pathogen of Brassicaceae-family plants, known now as Albugo candida = Cystopus candidus (Steinmetz 1954). No research could be identified regarding this theory, so it is unknown if it is true or itself a myth.
References
Danesh AS, Mojab F, Mohammadbeigi A, et al. (2019) "The effect of Capsella bursa-pastoris extract on heavy menstrual bleeding and quality of life in patients with uterine leiomyoma: A double-blind randomized clinical trial" J Pharm Res Int 31(3):1–10 (JPRI.51415).
Ghalandari S, Kariman N, Sheikhan Z, et al. (2017) "Effect of hydroalcoholic extract of Capsella bursa pastoris on early postpartum hemorrhage: A clinical trial study" J Altern Complement Med 23(10):794–9.
Neagu E, Paun G, Ungureanu O, Radu GL (2019) "Antioxidant activity and phenolics content of Capsella bursa-pastoris and Marrubium vulgare depending on environmental factors" Environ Engineer Manage J 18(7):1553–60.
Steinmetz EF (1954) Materia Medica Vegetabilis (Amsterdam: self-published).
Danesh AS, Mojab F, Mohammadbeigi A, et al. (2019) "The effect of Capsella bursa-pastoris extract on heavy menstrual bleeding and quality of life in patients with uterine leiomyoma: A double-blind randomized clinical trial" J Pharm Res Int 31(3):1–10 (JPRI.51415).
Ghalandari S, Kariman N, Sheikhan Z, et al. (2017) "Effect of hydroalcoholic extract of Capsella bursa pastoris on early postpartum hemorrhage: A clinical trial study" J Altern Complement Med 23(10):794–9.
Neagu E, Paun G, Ungureanu O, Radu GL (2019) "Antioxidant activity and phenolics content of Capsella bursa-pastoris and Marrubium vulgare depending on environmental factors" Environ Engineer Manage J 18(7):1553–60.
Steinmetz EF (1954) Materia Medica Vegetabilis (Amsterdam: self-published).