Lemon Myrtle

Lemon Myrtle (Backhousia citriodora) is exceptionally rich in citral (>90% of essential oil) and the ellagitannin casuarinin, which confer potent antimicrobial, antioxidant, and anti-inflammatory activity via DPPH/ABTS radical scavenging and inhibition of nitric oxide production in LPS-stimulated macrophages (PMID 32071880). Its essential oil has also been shown to induce S-phase cell cycle arrest and apoptosis in HepG2 liver cancer cells (PMID 37054823), while a 2025 randomized controlled trial demonstrated that lemon myrtle extract enhances muscle hypertrophy in older adults undergoing resistance training (PMID 41076797).

Origin & History

Lemon Myrtle (Backhousia citriodora) is an aromatic evergreen shrub belonging to the Myrtaceae family, native to the subtropical rainforests of central and southeastern Queensland, Australia. It thrives in well-drained soils with ample sunlight and high humidity. Its leaves are highly valued for their potent antimicrobial, immune-enhancing, and respiratory-supporting properties.

Historical & Cultural Context

Lemon Myrtle has been a vital part of Indigenous Australian healing traditions for generations, revered as the "Queen of the lemon herbs" for purifying the body, enhancing respiratory clarity, and strengthening immunity. It was traditionally used in bush medicine for infections, respiratory support, and digestive comfort, as well as in ceremonial practices.

Health Benefits

- **Enhances immune resilience**: through potent antimicrobial, antiviral, and antifungal activity, primarily from citral.
- **Supports respiratory health**: by acting as an expectorant, clearing congestion and soothing airways.
- **Promotes digestive balance**: and reduces gut discomfort through carminative effects.
- **Provides powerful antioxidant**: protection against oxidative stress and cellular damage via polyphenols and quercetin.
- **Aids in cognitive**: clarity and mood enhancement by reducing stress and anxiety.

How It Works

Lemon myrtle's primary bioactive compound, citral (a mixture of geranial and neral), disrupts microbial cell membranes and inhibits key enzymatic pathways in bacteria, fungi, and viruses, underpinning its broad-spectrum antimicrobial activity. The ellagitannin casuarinin and flavonoids including quercetin exert antioxidant effects through direct scavenging of DPPH and ABTS radicals, with ABTS scavenging activity documented to increase from 35.21% to 60.32% under optimized extraction conditions (PMID 32071880). Anti-inflammatory mechanisms involve suppression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression, leading to reduced nitric oxide and prostaglandin E2 production in LPS-stimulated RAW 264.7 macrophages. In HepG2 cells, lemon myrtle essential oil activates caspase-3/9-dependent intrinsic apoptotic pathways and arrests the cell cycle at S-phase by modulating cyclin A and CDK2 expression (PMID 37054823).

Scientific Research

A 2020 study in Toxicology Reports demonstrated that Backhousia citriodora leaf extract exhibits significant anti-inflammatory activity by suppressing nitric oxide and prostaglandin E2 production in LPS-stimulated RAW 264.7 macrophages, alongside strong DPPH and ABTS radical scavenging capacity (Shim SY et al., PMID 32071880). Wang et al. (2023) in the Journal of Ethnopharmacology showed that lemon myrtle essential oil induces S-phase cell cycle arrest and triggers caspase-dependent apoptosis in HepG2 hepatocellular carcinoma cells, suggesting anticancer potential (PMID 37054823). A 2024 zebrafish toxicological screening in Antioxidants confirmed the phytochemical richness and safety profile of lemon myrtle extracts at relevant doses (Cáceres-Vélez PR et al., PMID 39199222). Notably, Sawada et al. (2025) published findings from two independent randomized controlled trials in the Journal of Nutrition, Health and Aging showing that lemon myrtle extract significantly enhances muscle hypertrophy induced by low-load bodyweight resistance training in older adults (PMID 41076797).

Clinical Summary

Current evidence is limited to in vitro and preliminary animal studies, with no human clinical trials reported. Laboratory studies demonstrate significant anti-inflammatory effects with extracts at 20 μg/mL inhibiting nitric oxide production in macrophage cells (P < 0.05). Cell culture studies show no cytotoxicity up to 100 μg/mL concentrations, while satellite cell activation studies confirmed casuarinin's muscle-promoting effects (p < 0.05). The antimicrobial and antioxidant claims require validation through controlled human clinical trials to establish therapeutic efficacy and optimal dosing protocols.

Nutritional Profile

- Essential Oil: Citral (80-98%) (antimicrobial, antiviral, mood-enhancing, respiratory support)
- Phytochemicals: Flavonoids, Polyphenols, Quercetin (antioxidant, anti-inflammatory, immune modulation)
- Terpenes: Linalool, Pinene, Myrcene (calming, immune-modulating, digestive support)
- Vitamins: A, C, E (immune resilience, collagen synthesis, cellular protection)
- Minerals: Calcium, Magnesium, Potassium (nerve function, muscle relaxation, electrolyte balance)
- Other Bioactives: Tannins, Saponins (gut support, detoxifying effects)

Preparation & Dosage

- Tea: Steep 1–2 teaspoons (5–10g) of dried leaves in hot water for immune and respiratory benefits.
- Extract/Powder: Consume 500–1,500 mg of extract daily in supplements or functional foods.
- Topical: Infuse into balms or oils for antiseptic and anti-inflammatory skin applications.
- Aromatherapy: Use essential oil in diffusers or steam inhalations for respiratory and mood support.

Synergy & Pairings

Role: Polyphenol/antioxidant base
Intention: Immune & Inflammation | Respiratory & Circulation
Primary Pairings: - Eucalyptus (Eucalyptus globulus)
- Ginger (Zingiber officinale)
- Peppermint (Mentha piperita)
- Elderberry (Sambucus nigra)

Safety & Interactions

Zebrafish larval toxicological screening (PMID 39199222) confirmed that lemon myrtle extracts demonstrate a favorable safety profile at nutritionally relevant concentrations, though high doses of concentrated essential oil may cause mucosal irritation due to elevated citral content. Citral is a known contact sensitizer in susceptible individuals, and topical application of undiluted lemon myrtle oil should be avoided to prevent dermatitis. While no specific CYP450 interaction studies have been published for Backhousia citriodora, citral has been shown in preclinical models to modulate CYP2B6 activity, suggesting caution when co-administered with drugs metabolized by this enzyme. Pregnant and breastfeeding women should consult a healthcare provider before using concentrated lemon myrtle supplements, as high-dose citral has demonstrated uterotonic effects in animal models.