Manuka

What Is Manuka?

In New Zealand, where manuka trees grow, the Maori consider male tea tree plants “Kanuka” and the female plants “Manuka”. The plant is regarded very highly in this culture as a medicinal species.

The most well-known form of manuka is in manuka honey. This is a honey made by bees feasting primarily on manuka bushes. The honey has an impressive antibacterial profile when made from these plants. This is also reflected in the herb itself, which has been shown to have potent antibacterial, anti-fungal, and antiviral activity.

Most of the medicinal benefits of the plant come from its essential oil content, which can vary a lot depending on the region the plant was grown in.

What Is Manuka Used For?

Internally, manuka is used to treat gastrointestinal conditions like diarrhea, colic, inflammatory bowel syndrome, and dysentery. It’s also used for urinary tract infection, anxiety, and cold/flu infections.

Manuka is used topically for its antibacterial, and vulnerary actions. It’s used to treat slow healing skin and bone injuries, bacterial infections, candida, and eczema. It can be gargled for gingivitis, or for general oral hygiene.

Manuka honey is another common form of the plant. It’s become so popular worldwide, it’s been standardised by the phenol content. This is expressed as a unique manuka factor (UMF) value set by the Active Manuka Honey Association (AMHA). Anything over UMF 5 is considered strong enough to kill MRSA.

Botanical Information

Manuka is a member of the Myrtaceae family of plants. This family contains as many as 133 different genera, and around 3800 different species, many of which are medicinally relevant.

Phytochemistry

Manuka’s medicine is largely an essential-oil story, and that oil is dominated by two fractions. The first is a set of cyclic β-triketones — chiefly leptospermone, with isoleptospermone and flavesone — which together account for roughly 20% of the oil (often 20–33% in the prized East Cape “triketone” chemotype) and carry the bulk of its antibacterial and antifungal punch. The second is a heavy load of sesquiterpene hydrocarbons (≥60% of the oil), led by trans-calamenene (mean ~12.5%) alongside cadinene- and copaene-type compounds.

Manuka oil is highly chemotype-dependent: a far-north form is rich in pinene, the East Cape form is high-triketone, and South Island plants run high in sesquiterpenes (up to ~65%). Minor citronellal and astringent tannins round out the leaf.

It is worth separating the oil from the famous honey. Manuka honey is a separate product whose non-peroxide antibacterial activity comes from methylglyoxal (MGO), formed from nectar-derived dihydroxyacetone as the honey matures — graded by the Unique Manuka Factor (UMF). MGO is a honey constituent, not a constituent of the plant tissue, so it is not tabled below.

Constituent Summary

Figures are share of the steam-distilled essential oil (mass %), pooled from GC studies of New Zealand oils; values vary widely by chemotype and region. Whole-oil yield from the leaf is ~0.2–1%.

Clinical Applications

Manuka is useful both internally and topically. It’s been shown to be an effective antibacterial agent for various forms of bacteria (including Staphylococcus). It’s also an effective anti-fungal and antiviral (including HSV). The antibacterial effects were the most notable, with only some chemotypes of Manuka showing potent anti-fungal benefits.

Manuka can be used for nearly any form of bacterial infections both topically and internally, as well as wounds, ulcers, and gastrointestinal inflammation or infection. It’s also useful for skin inflammation like eczema or psoriasis. The muscle relaxant effects make it useful for injuries, muscle tension, colic, and insomnia.

Cautions & Safety

Manuka is widely considered safe and there are no common side effects of the herb.

Contraindications

Avoid long-term use alongside food. Tannins may impede mineral absorption.

References

1. Porter, N. G., & Wilkins, A. L. (1998). Chemical, physical and antimicrobial properties of essential oils of Leptospermum scoparium and Kunzea ericoides. Phytochemistry, 50(3), 407-415.
2. Douglas, M. H., van Klink, J. W., Smallfield, B. M., Perry, N. B., Anderson, R. E., Johnstone, P., & Weavers, R. T. (2004). Essential oils from New Zealand manuka: triketone and other chemotypes of Leptospermum scoparium. Phytochemistry, 65(9), 1255-1264.
3. Mathew, C., Tesfaye, W., Rasmussen, P., Peterson, G. M., Bartholomaeus, A., Sharma, M., & Thomas, J. (2020). Mānuka Oil—A Review of Antimicrobial and Other Medicinal Properties. Pharmaceuticals, 13(11), 343.
4. Mavric, E., Wittmann, S., Barth, G., & Henle, T. (2008). Identification and quantification of methylglyoxal as the dominant antibacterial constituent of Manuka (Leptospermum scoparium) honeys from New Zealand. Molecular Nutrition & Food Research, 52(4), 483-489.