MANUKA: For Stress & Mood

Posted: June 2022
Author: Phil Rasmussen | M.Pharm., M.P.S., Dip. Herb. Med.; M.N.I.M.H.(UK),  F.N.Z.A.M.H. 
 

Mānuka (Leptospermum scoparium) is common throughout Aotearoa New Zealand and as medical herbalists in this country, we appreciate its value as a medicine and use it for a wide range of different clinical conditions.¹

The foliage, bark and seeds were all used by Māori as medicines prior to European colonisation, particularly as topical preparations for wounds, cuts, sores and skin diseases, and inhalations for colds and fevers. The use of mānuka as a tea and a substitute for Camellia sinensis was adopted by Cook’s sailors and became common during the 1800s. Interest in mānuka continues to increase, due largely to the popularity and medicinal properties of mānuka honey as well as its volatile oil, which has antimicrobial, anti-inflammatory and other useful applications.^{2, 3, 4}

Mānuka’s uses beyond those of the honey and oil, have always interested me greatly,^{1, 5} as has any research on this plant. Amongst the various traditional uses of mānuka documented by early European settlers to Aotearoa, was a report by Charles Goldie made in 1905 of “an infusion of the bark being used externally as a sedative”.⁶ However, little other information appears in the early literature on this application, and as with many traditional plant uses, our understanding of how and when it was used in this way is lacking.

In 1994 I came across a freshly published paper by German researchers which reported that the young twigs with juvenile leaves from mānuka contain flavonoids which interacted with benzodiazepine GABA-A receptors.⁷  Agonist activity and modulation of these receptors is intrinsic to the mechanisms of action of anxiolytic, sedative and anticonvulsant benzodiazepine drugs such as diazepam and clonazepam.  Locomotion studies in rats by the same researchers subsequently reported sedative activities for moderate doses of the mānuka extract they had prepared.⁸

At the time, I keenly embraced these reported findings and began to use mānuka leaf extracts in many of my patients with anxiety and stress-related conditions, though with little apparent benefits. I also notified researchers in New Zealand about the German work, who subsequently failed to locate the same types of methoxylated flavonoids in this plant. Sometime later, however, they found similar types of flavones in the oil glands of particular varieties of mānuka, which is also where the well-known antimicrobial β-triketones such as grandiflorine, were found to be compartmentalised.⁹

While most mānuka being harvested today comes from wildcrafted sources, increasingly we are seeing a plantation model being used to try and achieve higher grades and yields of honey or oil for commercial purposes. This has its merits but could also lead to the narrowing of the gene pool of different varieties, and so it is an area that needs monitoring in the future. It also, however, presents the opportunity to propagate and grow particular varieties whose leaves contain higher levels of specific phytochemicals that we as medical herbalists, value for the types of indications for which we prescribe and dispense extracts of this plant to our patients. Cultivating and harvesting to optimise levels of specific flavonoid compounds or tannins perhaps, and not just high β-triketones essential oil or active honey-yielding varieties. Once planted though, we should realise that the bees and other forces of nature will do their part to share and mix the gene pool around!

One common condition that is often triggered or exacerbated by stress and anxiety, is Irritable Bowel Syndrome (IBS). It can be challenging to treat, but my experience is that mānuka can be a very effective intervention, particularly in those where looseness of the bowels or diarrhoea is a feature. Apart from any potential anxiolytic or relaxant properties of its flavonoids, the established astringency of the tannins, antispasmodic activity of the volatile oil, and good antimicrobial activity of mānuka leaf extracts are all useful for the symptomatic relief of IBS-D. These actions can collectively make mānuka a very helpful treatment to help foster relaxation of that ‘second brain in the gut’ as well as more of a balance to our gut microbiome.

As we know there are a lot of stress-related conditions out there at present, and mānuka is one herb we should consider alongside our many other herbal extracts, as part of our treatment and management of patients with these. Stress-related conditions ranging from IBS, to nervous diarrhoea, and anxiety particularly where there is a digestive component, are often amenable.
 

References:

1. Rasmussen PL, Manuka (Leptospermum scoparium) – A Review. Phytonews 1, September 1998, published by Phytomed Medicinal Herbs Ltd, Auckland, New Zealand.    ISSN 1175-0251.
2. Mathew C, Tesfaye W, Rasmussen P, Peterson GM, Bartholomaeus A,, Sharma M, Thomas J.  Manuka Oil – a Review of antimicrobial and other medicinal properties. Pharmaceuticals 2020; 13:343-354.
3. Nolan, V. C., Harrison, J., Wright, J., & Cox, J. (2020). Clinical Significance of Manuka and Medical-Grade Honey for Antibiotic-Resistant Infections: A Systematic Review. Antibiotics (Basel, Switzerland), 9(11), 766.
4. Rasmussen PL, www.herbblurb.com ‘Manuka Oil as an alternative to antibiotic creams’, October 7, 2016.
5. Rasmussen PL, Manuka and Myrtle Rust. www.herbblurb.com July 19, 2017.
6. Goldie W.H., “Maori Medical Lore”, Trans. Proc. NZ Inst. Vol. 37, 1905.
7. Häberlein, H., & Tschiersch, K. P. (1994). 2,5-Dihydroxy-7-methoxy-6,8-dimethylflavan-3-one a novel flavonoid from Leptospermum scoparium: in vitro affinity to the benzodiazepine binding site of the GABAA receptor-chloride channel complex. Die Pharmazie, 49(11), 860.
8. Häberlein, H., Tschiersch, K. P., & Schäfer, H. L. (1994). Flavonoids from Leptospermum scoparium with affinity to the benzodiazepine receptor characterized by structure activity relationships and in vivo studies of a plant extract. Die Pharmazie, 49(12), 912–922.
9. Killeen, D. P., van Klink, J. W., Smallfield, B. M., Gordon, K. C., & Perry, N. B. (2015). Herbicidal β-triketones are compartmentalized in leaves of Leptospermum species: localization by Raman microscopy and rapid screening. The New phytologist, 205(1), 339–349.