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 19 Mar 2022

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.

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.

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.

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.