Hyunsuh Kim

Thriving with the Tiger Rod

Medical benefits of the invasive plant

In 2020, the Dutch government released 5,000 psyllids to combat the spread of Japanese knotweed. The plan is for the knotweed’s natural predator to devour the otherwise invincible species. As it happens, Japanese knotweed is also one of the most beloved herbs in East Asia for its medical properties. Why not join in the feast?


Not In My Backyard!, Kristof Vrancken & Niek Kosten - Night picture of a house surrounded by Japanese knotweed

“Judging by its primary benefits, the hojang (호장; 虎杖; “tiger rod”) is akin to cheonmyeongjeong (천명정; 天名精; Carpesium) in its aid in blood flow and similar to wangbulryuhaeng (왕불류행; 王不留行; Caryophyllaceae) in its healing of palsy. The ancient sages said that it is particularly effective in relieving heat stroke, for blood chases after the heat source and dissipates the warmth. Hence applying it to the ills relating to the blood plasma at the pericardium meridian of hand* (手厥陰) or the wind at the liver meridian of foot** (足厥陰), one can witness effects as immediate as sound which follows the hitting of drums. Medical prescriptions detail its ability to clear out heat of all kinds at times of spams, so why limit its use in other cases? Prescriptions also recount its uses in treating urinary retention. Zhu Zhenheng also used hojang in treating urinary retention in the elderly and made restorative tonics with it. It is said that those who are weakened must avoid using the herb lest it cause harm, but would that be a concern if it was used alongside other roborant ingredients?”

Enthuses Bonchosul (본초술; 本草述; “Use of Medicinal Herbs”), a herbology book compiled in 1694, late Joseon Dynasty, based on older theories of Chinese medicine and experiences of contemporary practitioners. It describes the wide range of use for Japanese knotweed, named the “tiger rod” for the dotted patterns on its stalk. 

Two key substances in Japanese knotweed, emodin and trans-reservatrol, have antimicrobial properties against a wide range of bacteria, viruses, fungi and protozoa. As these substances pass across the blood-brain barrier, Japanese knotweed has raised interesting potentials for the health of the brain microbiome (Rawls). 

Furthermore, trans-resveratrol is an active form of resveratrol that behaves as a natural antioxidant, aiding the protection of immune and cardiovascular systems. Japanese knotweed extract was shown to increase T-cells, B-cells, monocyte and macrophage markers in addition to further stimulating phagocytic activity of the macrophages in mice (Chueh et al.). As enhancement of the immune system reduces inflammation, this decreases the risk of plaque buildup and atherosclerosis (Liu et al.). For this reason, the herb is called itadori (イタドリ; “take away pain”) in Japan.

More ecologists are adopting the idea that not all invasive plants are destructive, partly due to the concerns regarding the ecological impacts of eradication efforts such as the use of chemicals. They contend that “ ‘invasion’ is just another word for ‘change’ ” which will only increase due to globalization (Goode). On the other hand, Japanese knotweed has a less than beneficial impact on the environment. The particularly fecund variety of the species (read our previous blog post on the history of Japanese knotweed in Europe) destabilizes the riparian ecosystems and increases the risk of soil erosion and flooding by outcompeting the existing vegetation that holds the soil (Matte et al.). At the same time, its impact in the urban setting is often exaggerated (Fennell et al.), causing unnecessary stress on house owners.

A variety of means has been used to eradicate Japanese knotweed across Europe: cutting, herbicide, electrocution, lazer, and in the case of the Netherlands, knotweed psyllids, also a foreign species (Coles). An easier and healthier way to deal with this persistent neighbor of ours may be to invite it to our dinner table. Here is a suggestion from Yakseongron (약성론; 藥性論; “Theories of Medicinal Properties”) for the coming summer:

“Boil hojang with gamcho (감초; 甘草; Chinese liquorice) in the summer and it turns into an aromatic tonic with a beautiful shade of amber. Keep the earthenware jar in the well to cool it down, and drink it ice-cold in white porcelain or silver bowl as you would tea. Modern men call it ‘cooling beverage’ and regard it with an even higher regard than tea made with the young shoots of the plant.” 

* One of the twelve meridians, the paths of qi (氣) in traditional Chinese medicine, the pericardium meridian begins in the thorax, connects with the pericardium, and to the lower abdomen.

** The liver meridian travels along the medial aspect of the leg, passes over the chest and abdomen, connecting the liver with the gallbladder


Not In My Backyard!, Kristof Vrancken & Niek Kosten - Night picture of Japanese knotweed by a highway


Chueh, F, et al. (2015). Crude extract of Polygonum cuspidatum stimulates immune responses in normal mice by increasing the percentage of Mac-3-positive cells and enhancing macrophage phagocytic activity and natural killer cell cytotoxicity. Molecular Medicine Reports 11(1), 127–132. doi: 10.3892/mmr.2014.2739.

Coles, W. “Natural enemy shows early promise in fight against Japanese knotweed in the Netherlands.” CABI, 6 Dec. 2021, https://blog.invasive-species.org/2021/12/06/natural-enemy-shows-early-promise-in-fight-against-japanese-knotweed-in-the-netherlands/

Fennell M, Wade M, Bacon KL. (2018). Japanese knotweed (Fallopia japonica): an analysis of capacity to cause structural damage (compared to other plants) and typical rhizome extension. Peer Journal Life and Environment, 25;6:e5246. doi: 10.7717/peerj.5246.

Goode, E. “Invasive Species Aren’t Always Unwanted.” The New York Times, 29 Feb. 2016, https://www.nytimes.com/2016/03/01/science/invasive-species.html

Kim, Nam, Y., Song, J., & Kim, H. (2020). Gastroprotective and healing effects of Polygonum cuspidatum root on experimentally induced gastric ulcers in rats. Nutrients, 12(8), 2241–. doi:10.3390/nu12082241

Liu LT, Zheng GJ, Zhang WG, Guo G, Wu M. (2014). Clinical study on treatment of carotid atherosclerosis with extraction of polygoni cuspidati rhizoma et radix and crataegi fructus: a randomized controlled trial. China Journal of Chinese Materia Medica, 39(6),1115-1119. PMID: 24956862.

Matte, R., Boivin, M., & Lavoie, C. (2022). Japanese knotweed increases soil erosion on riverbanks. River Research and Applications, 38(3), 561-572. doi:10.1002/rra.3918.

Rawls, B. “Japanese knotweed, resveratrol.” Vital Plan. https://vitalplan.com/ingredients/resveratrol

“호장근 무엇인가?” 한국 토종 야생 산야초 연구소. http://jdm0777.com/jdm/hojanggeun.htm