Herb Garden

Antimicrobial Activity and Immune Support
Manuka leaf has a long history of use by the Māori people of New Zealand for its broad-spectrum antimicrobial capabilities. The primary mechanism of action is attributed to unique β-triketone compounds—specifically leptospermone, isoleptospermone, and flavesone—which are found in high concentrations in the leaf oil.[1,2] Comparative studies have demonstrated that Manuka leaf extracts exhibit significantly stronger inhibitory effects against Gram-positive bacteria, such as Staphylococcus aureus, than the related Australian Tea Tree oil (Melaleuca alternifolia).[3] Research indicates that these triketones disrupt the bacterial cell membrane, leading to cell lysis and preventing bacterial proliferation.[4] Furthermore, in vitro studies suggest that Manuka leaf extracts can enhance the activity of antibiotics against resistant strains (such as MRSA), making it a powerful botanical ally for immune defense.[5]

Digestive Health and Spasmolytic Effects
Beyond its antimicrobial prowess, Manuka leaf offers significant benefits for gastrointestinal health. Traditional infusions of the leaves were widely used to treat dysentery, diarrhea, and colic. Modern pharmacological assessments support these applications, identifying spasmolytic (anti-spasmodic) activity in the leaf extract that helps relax smooth muscle contraction in the gut. [6] This effect is likely mediated by the plant's flavonoid and terpene content, particularly β-caryophyllene, which also exhibits potent anti-inflammatory properties. [7] By reducing intestinal inflammation and oxidative stress, Manuka leaf helps maintain mucosal integrity and soothe digestive discomfort. [8] Additionally, the antioxidant capacity of the leaf extract has been measured to be superior to standard reference compounds in neutralizing free radicals, further protecting the digestive tract from cellular damage. [9]

Toxicity
Manuka leaf and its essential oil are generally considered safe for consumption in supplement form. Toxicology studies indicate a high safety margin, with acute oral LD50 values in rats reported at >2,000 mg/kg to >9,000 mg/kg, classifying it as essentially non-toxic. [10,11] While the concentrated essential oil can be irritating to the skin at high doses, the whole-leaf extracts used in dietary supplements typically fall well within safety guidelines. No genotoxicity or mutagenicity has been observed in standard assays. [12]