1,8-cineole

Pharmacology & Research

1,8-Cineole (eucalyptol) is a bicyclic monoterpenoid ether — the fresh, camphoraceous principal of eucalyptus oil and a major volatile of rosemary, cardamom, sage and bay. It stands out among plant terpenes for one reason: unlike most essential-oil constituents, whose human evidence is aromatherapy or whole-oil, cineole has genuine double-blind, placebo-controlled trials of the isolated molecule — standardised 200 mg gut-soluble capsules (marketed as “Cineole”/Soledum) tested in COPD, asthma, acute bronchitis and rhinosinusitis ^{1,2,3,4,5Reference 1Worth H et al. · 2009RCTConcomitant therapy with Cineole (Eucalyptole) reduces exacerbations in COPD: a placebo-controlled double-blind trial — randomised controlled trialView study →Reference 2Juergens UR et al. · 2003RCTAnti-inflammatory activity of 1.8-cineol (eucalyptol) in bronchial asthma: a double-blind placebo-controlled trial — randomised controlled trialView study →Reference 3Worth H · 2012RCTPatients with asthma benefit from concomitant therapy with cineole: a placebo-controlled, double-blind trial — randomised controlled trialView study →Reference 4Kehrl W et al. · 2004RCTTherapy for acute nonpurulent rhinosinusitis with cineole: results of a double-blind, randomized, placebo-controlled trial — randomised controlled trialView study →Reference 5Fischer J · 2013RCTEfficacy of cineole in patients suffering from acute bronchitis: a placebo-controlled double-blind trial — randomised controlled trialView study →}. Mechanistically it behaves as a mucolytic and anti-inflammatory, suppressing cytokine and arachidonic-acid-mediator production in human immune cells ^{6,7Reference 6Juergens UR et al. · 1998Antiinflammatory effects of eucalyptol (1.8-cineole) in bronchial asthma: inhibition of arachidonic acid metabolism in human blood monocytes ex vivoView study →Reference 7Juergens UR et al. · 2004In vitroInhibitory activity of 1,8-cineol (eucalyptol) on cytokine production in cultured human lymphocytes and monocytes — in vitroView study →}. Two caveats frame the rest: the respiratory trials cluster around a small set of overlapping investigators, and pharmacokinetically cineole is both a CYP3A substrate and an inducer of hepatic drug-metabolising P450s — an interaction-relevant profile, and the same molecule that makes concentrated eucalyptus oil neurotoxic when swallowed in bulk ^{8,11,12Reference 8Cai ZM et al. · 2021ReviewCai ZM, Peng JQ, Chen Y, Tao L, Zhang YY, Fu LY, Long QD, Shen XC. (2021). 1,8-Cineole: a review of source, biological activities, and application — review. Journal of Asian Natural Products Research, 23(10), 938–954. https://pubmed.ncbi.nlm.nih.gov/33111547/View study →Reference 11Miyazawa M et al. · 2001AnimalOxidation of 1,8-cineole, the monoterpene cyclic ether originated from Eucalyptus polybractea, by cytochrome P450 3A enzymes in rat and human liver microsomesView study →Reference 12Jori A et al. · 1972On the inducing activity of eucalyptol — animal studyView study →}.

1. COPD (exacerbation reduction)

The strongest single line, and a genuine isolate result. In a double-blind, placebo-controlled multicentre trial, 242 patients with stable COPD received 200 mg of isolated cineole or placebo three times daily for six months as concomitant therapy; the cineole group had significantly fewer, shorter and less severe exacerbations, with improvements in lung function, dyspnoea and quality of life and adverse-event rates comparable to placebo ^{1Reference 1Worth H et al. · 2009RCTConcomitant therapy with Cineole (Eucalyptole) reduces exacerbations in COPD: a placebo-controlled double-blind trial — randomised controlled trialView study →}. The authors frame cineole as an active controller of airway inflammation acting on the mucus membrane, consistent with its mucolytic/anti-inflammatory mechanism ^{1,6Reference 1Worth H et al. · 2009RCTConcomitant therapy with Cineole (Eucalyptole) reduces exacerbations in COPD: a placebo-controlled double-blind trial — randomised controlled trialView study →Reference 6Juergens UR et al. · 1998Antiinflammatory effects of eucalyptol (1.8-cineole) in bronchial asthma: inhibition of arachidonic acid metabolism in human blood monocytes ex vivoView study →}.

Gap: a single six-month trial from the same research group that ran the asthma and bronchitis studies; no independent replication or hard mortality/hospitalisation endpoints.

2. Asthma (steroid-sparing)

Two double-blind, placebo-controlled trials of the isolate. In 32 patients with steroid-dependent severe asthma, 200 mg cineole three times daily for 12 weeks allowed a significantly greater reduction in oral prednisolone dose than placebo (36% vs 7%; 12/16 vs 4/16 patients able to taper) — the first evidence of a glucocorticoid-sparing, anti-inflammatory action for the molecule ^{2Reference 2Juergens UR et al. · 2003RCTAnti-inflammatory activity of 1.8-cineol (eucalyptol) in bronchial asthma: a double-blind placebo-controlled trial — randomised controlled trialView study →}. A separate trial in 247 asthma patients found 200 mg three times daily improved FEV1, symptoms and asthma quality-of-life versus placebo over six months ^{3Reference 3Worth H · 2012RCTPatients with asthma benefit from concomitant therapy with cineole: a placebo-controlled, double-blind trial — randomised controlled trialView study →}.

Gap: small (steroid-sparing) and single trials; again clustered around the same investigators, and not incorporated into major asthma guidelines.

3. Acute bronchitis

In a double-blind, placebo-controlled multicentre trial, 242 patients with acute bronchitis took 200 mg cineole or placebo three times daily; the cineole group improved on a bronchitis sum-score significantly more than placebo after just four days, with the largest effect on frequency of coughing fits (p = 0.0001) ^{5Reference 5Fischer J · 2013RCTEfficacy of cineole in patients suffering from acute bronchitis: a placebo-controlled double-blind trial — randomised controlled trialView study →}. The isolate again reads as an anti-inflammatory/mucolytic, shortening symptomatic illness.

Gap: a symptom-score endpoint over a short, self-limiting illness; no effect on antibiotic use or hard outcomes shown, and single-group provenance.

4. Acute rhinosinusitis

In 152 patients with acute non-purulent rhinosinusitis, cineole capsules (two 100 mg capsules three times daily, i.e. 600 mg/day) reduced a defined symptoms-sum-score significantly more than placebo by days 4 and 7, across headache, nasal obstruction and secretion, with only mild side effects (heartburn, exanthema in two patients) — positioned as effective treatment before antibiotics are indicated ^{4Reference 4Kehrl W et al. · 2004RCTTherapy for acute nonpurulent rhinosinusitis with cineole: results of a double-blind, randomized, placebo-controlled trial — randomised controlled trialView study →}.

Gap: a seven-day symptom-score trial in a largely self-resolving condition; no imaging or microbiological endpoints, and the same isolate-vs-plant strength/limitation (real molecule, one trial).

5. Antimicrobial

Cineole has broad in-vitro antibacterial and antifungal activity, generally attributed to disruption of microbial membrane integrity, and cineole-rich eucalyptus oil is among the more active essential oils against Staphylococcus aureus and streptococci in comparative assays ^{8,16Reference 8Cai ZM et al. · 2021ReviewCai ZM, Peng JQ, Chen Y, Tao L, Zhang YY, Fu LY, Long QD, Shen XC. (2021). 1,8-Cineole: a review of source, biological activities, and application — review. Journal of Asian Natural Products Research, 23(10), 938–954. https://pubmed.ncbi.nlm.nih.gov/33111547/View study →Reference 16Sataie-Mokhtari T et al. · 2026In vitroGC-MS based chemical composition and in vitro antibacterial activity of the essential oils of Eucalyptus cultivarsView study →}. This is the traditional “antiseptic eucalyptus” reputation given a mechanistic gloss.

Gap: almost entirely in-vitro and largely whole-oil rather than isolated cineole; standalone potency is modest relative to phenolic EO constituents, and there is no antimicrobial human trial of the isolate.

6. Cognition & alertness

In 20 healthy volunteers exposed to diffused rosemary aroma, higher plasma 1,8-cineole absorbed from the aroma correlated with better speed and accuracy on serial-subtraction and visual-processing tasks (not a speed–accuracy trade-off), with weaker links to mood ^{14Reference 14Moss M · 2012Clinical trialPlasma 1,8-cineole correlates with cognitive performance following exposure to rosemary essential oil aroma — human studyView study →}. This is the best human bridge between the molecule and the “alerting” reputation of cineole-rich oils.

Gap: correlational, small, and the exposure vehicle is a whole plant essential oil (rosemary), so this is not an isolated-cineole efficacy trial — cineole is a plausible mediator, not a proven one.

Mechanisms

Target / pathway	Effect	Relevant to
NF-κB / cytokine production (TNF-α, IL-1β, IL-6, IL-8)	Suppressed in human monocytes & lymphocytes	asthma, COPD, anti-inflammatory
Arachidonic-acid metabolism (LTB4 via 5-LOX; PGE2 via COX)	Both pathways inhibited ex vivo	asthma, mucosal inflammation
Airway mucus / secretory epithelium	Mucolytic / secretolytic; ↓ hypersecretion	bronchitis, COPD, rhinosinusitis
Airway smooth muscle	Bronchodilating / spasmolytic	asthma, COPD
CYP3A (substrate) + hepatic P450 induction	Oxidised by CYP3A; induces drug-metabolising P450s (animal)	drug interactions, pharmacokinetics
Microbial membranes	Membrane disruption (whole-oil / in-vitro)	antimicrobial

Pharmacokinetics

Cineole’s pharmacokinetics are the compound page’s core value-add, and they carry the interaction story. It is well absorbed: during human inhalation it reaches peak plasma at about 18 minutes, with a rapid distribution half-life (~6.7 min) and a terminal elimination half-life around 104 minutes ^{9Reference 9Jäger W et al. · 1996Pharmacokinetic studies of the fragrance compound 1,8-cineol in humans during inhalation — human pharmacokinetic studyView study →}. Given orally (studied via sage tea), it is rapidly and extensively hydroxylated by cytochrome P450 to 2-, 3-, 7- and 9-hydroxy-1,8-cineole and then glucuronidated; the parent compound stays at low plasma concentration while 2-hydroxycineole predominates, and roughly half the dose is recovered in urine as hydroxycineole metabolites within 10 hours ^{10Reference 10Horst K · 2010Quantification of 1,8-cineole and of its metabolites in humans using stable isotope dilution assays — human pharmacokinetic studyView study →}. Human liver microsome work identifies CYP3A as a principal oxidiser of cineole ^{11Reference 11Miyazawa M et al. · 2001AnimalOxidation of 1,8-cineole, the monoterpene cyclic ether originated from Eucalyptus polybractea, by cytochrome P450 3A enzymes in rat and human liver microsomesView study →}. The interaction-relevant twist is that cineole is not only a CYP substrate but a CYP inducer: it up-regulates hepatic drug-metabolising P450s in classic and later animal studies ^{12,13Reference 12Jori A et al. · 1972On the inducing activity of eucalyptol — animal studyView study →Reference 13Madyastha KM · 1986AnimalMetabolism of 1,8-cineole in rat: its effects on liver and lung microsomal cytochrome P-450 systems — animal studyView study →}, so co-administration could, in principle, accelerate the clearance of CYP-metabolised drugs. Human enzyme-induction data are limited, so this is a mechanism-based caution rather than a quantified clinical interaction.

Clinical trials

Unusually for a plant terpene, several investigator-led double-blind RCTs of the isolated molecule have been completed — all respiratory (COPD, asthma, acute bronchitis, rhinosinusitis) and largely from an overlapping German research network — but as an off-patent natural product it attracts little registered industry-sponsored trial activity.

Last checked: July 2026.

Isolate vs. Plant Studies

Cineole is the rare essential-oil constituent whose human evidence is mostly the isolated molecule, not a plant standing in for it. The COPD, asthma, bronchitis and rhinosinusitis trials all used standardised 200 mg cineole capsules (“Cineole”/Soledum), so their results genuinely describe the compound rather than a eucalyptus preparation ^{1,2,3,4,5Reference 1Worth H et al. · 2009RCTConcomitant therapy with Cineole (Eucalyptole) reduces exacerbations in COPD: a placebo-controlled double-blind trial — randomised controlled trialView study →Reference 2Juergens UR et al. · 2003RCTAnti-inflammatory activity of 1.8-cineol (eucalyptol) in bronchial asthma: a double-blind placebo-controlled trial — randomised controlled trialView study →Reference 3Worth H · 2012RCTPatients with asthma benefit from concomitant therapy with cineole: a placebo-controlled, double-blind trial — randomised controlled trialView study →Reference 4Kehrl W et al. · 2004RCTTherapy for acute nonpurulent rhinosinusitis with cineole: results of a double-blind, randomized, placebo-controlled trial — randomised controlled trialView study →Reference 5Fischer J · 2013RCTEfficacy of cineole in patients suffering from acute bronchitis: a placebo-controlled double-blind trial — randomised controlled trialView study →} — a real strength, and the reason cineole rates higher here than sibling terpenes like α-pinene whose human data are inhalation pharmacokinetics only. The mechanistic monocyte/lymphocyte work is likewise on isolated cineole ^{6,7Reference 6Juergens UR et al. · 1998Antiinflammatory effects of eucalyptol (1.8-cineole) in bronchial asthma: inhibition of arachidonic acid metabolism in human blood monocytes ex vivoView study →Reference 7Juergens UR et al. · 2004In vitroInhibitory activity of 1,8-cineol (eucalyptol) on cytokine production in cultured human lymphocytes and monocytes — in vitroView study →}. The main plant-vehicle exception is the cognition finding, where the exposure was whole rosemary aroma and cineole was measured as a correlate, not administered alone ^{14Reference 14Moss M · 2012Clinical trialPlasma 1,8-cineole correlates with cognitive performance following exposure to rosemary essential oil aroma — human studyView study →}; and the antimicrobial literature is largely whole eucalyptus oil ^{16Reference 16Sataie-Mokhtari T et al. · 2026In vitroGC-MS based chemical composition and in vitro antibacterial activity of the essential oils of Eucalyptus cultivarsView study →}. The whole-plant relationship also runs the other way: the expectorant reputation of rosemary, peppermint, hyssop and yerba santa is often attributed to cineole, but those oils are chemically complex, so a whole-oil effect cannot be pinned on cineole alone.

Prevalence in Nature

1,8-Cineole is one of the most widespread oxygenated monoterpenes in the plant kingdom, produced across the Myrtaceae (Eucalyptus, Melaleuca/tea tree), Lamiaceae (rosemary, sage, lavender, hyssop, catnip), Asteraceae (yarrow, wormwood), Zingiberaceae (cardamom) and Lauraceae (bay, rosewood) ^{8Reference 8Cai ZM et al. · 2021ReviewCai ZM, Peng JQ, Chen Y, Tao L, Zhang YY, Fu LY, Long QD, Shen XC. (2021). 1,8-Cineole: a review of source, biological activities, and application — review. Journal of Asian Natural Products Research, 23(10), 938–954. https://pubmed.ncbi.nlm.nih.gov/33111547/View study →}. Its marquee — and namesake — source is Eucalyptus: in Eucalyptus globulus leaf oil cineole is the dominant compound, measured at around 83.5% of the essential oil, and pharmaceutical-grade eucalyptus oil is standardised to a high cineole content ^{16Reference 16Sataie-Mokhtari T et al. · 2026In vitroGC-MS based chemical composition and in vitro antibacterial activity of the essential oils of Eucalyptus cultivarsView study →}. It is also the defining marker of the rosemary “cineole chemotype” (roughly 15–55% of the oil, occasionally higher) ^{17Reference 17Satyal P et al. · 2017Chemotypic characterization and biological activity of Rosmarinus officinalisView study →}, a major oxygenated monoterpenoid of cardamom seed oil (~25–31%) ^{18Reference 18Wanna R et al. · 2024Chemical compositions and fumigation effects of essential oils derived from cardamom (Elettaria cardamomum) and galangal (Alpinia galanga)View study →}, and a consistent minor-to-moderate component of sage (~9–11%) ^{19Reference 19Milenković L et al. · 2025Does photoselective netting influence yield, chemical composition and antioxidant activities of essential oils in cultivated sage? Frontiers in Plant Science, 16, 1540520. https://pubmed.ncbi.nlm.nih.gov/40365559/View study →} and peppermint (~3.5–14%) ^{21Reference 21European PharmacopoeiaReviewPeppermint oil (Menthae piperitae aetheroleum) monograph — gas-chromatographic composition limits, 1,8-cineole 3.5–14.0%}.

Concentration is dominated by chemotype and plant part rather than species alone: rosemary occurs as cineole-, camphor- and verbenone-dominant chemotypes that are chemically distinct oils ^{17Reference 17Satyal P et al. · 2017Chemotypic characterization and biological activity of Rosmarinus officinalisView study →}, and in true lavender cineole is normally minor — elevated levels flag adulteration with spike lavender or lavandin. Biosynthetically, cineole is a plastidial monoterpene formed from geranyl diphosphate: a 1,8-cineole synthase cyclises the universal monoterpene precursor to the bicyclic ether in a single enzymatic step, and the enzyme’s abundance and specificity are what make some oils cineole-rich. Cineole is essentially a plant (and to a lesser extent fungal) product, with no established animal biosynthesis.

Discovery & Synthesis

1,8-Cineole was characterised from eucalyptus oil in the nineteenth century, and the common name “eucalyptol” — reflecting its source rather than its structure — is generally attributed to French chemistry of around 1870; the precise first-isolation date is not cleanly pinned in the modern literature (see the gaps note). Today the molecule is essentially never made by total synthesis for commercial use: it is obtained by fractional distillation and rectification of eucalyptus oil (chiefly from Eucalyptus globulus and high-cineole species such as E. polybractea), which is so rich in cineole that fractionation to pharmaceutical grade (and the standardised capsules used in the clinical trials) is far cheaper than synthesis ^{8,16Reference 8Cai ZM et al. · 2021ReviewCai ZM, Peng JQ, Chen Y, Tao L, Zhang YY, Fu LY, Long QD, Shen XC. (2021). 1,8-Cineole: a review of source, biological activities, and application — review. Journal of Asian Natural Products Research, 23(10), 938–954. https://pubmed.ncbi.nlm.nih.gov/33111547/View study →Reference 16Sataie-Mokhtari T et al. · 2026In vitroGC-MS based chemical composition and in vitro antibacterial activity of the essential oils of Eucalyptus cultivarsView study →}. Cineole-rich oils from rosemary, cardamom and Melaleuca are secondary natural sources.

Patents: not yet researched (future patent-loop pass).

Toxicity & Safety

At the isolated therapeutic dose used in trials (200 mg three times daily), cineole was well tolerated, with adverse events comparable to placebo and only mild effects such as heartburn reported ^{1,4Reference 1Worth H et al. · 2009RCTConcomitant therapy with Cineole (Eucalyptole) reduces exacerbations in COPD: a placebo-controlled double-blind trial — randomised controlled trialView study →Reference 4Kehrl W et al. · 2004RCTTherapy for acute nonpurulent rhinosinusitis with cineole: results of a double-blind, randomized, placebo-controlled trial — randomised controlled trialView study →}. The safety concern is dose- and preparation-dependent, and it is an isolate-vs-plant story in reverse: cineole is the principal toxic constituent of concentrated eucalyptus oil, and ingestion of eucalyptus oil in bulk causes dose-dependent central-nervous-system toxicity — drowsiness, ataxia, vomiting and, at higher doses, seizures. This is well described in children, in whom depressed consciousness and seizures are the classic picture, and even adults who swallow large amounts can present with seizures and severe metabolic acidosis ^{15Reference 15Ittyachen AM et al. · 2019Case reportEucalyptus oil poisoning: two case reports — case reportView study →}. The practical rule that follows is longstanding: cineole-rich (eucalyptus-type) oils should never be applied on or near the face or nostrils of infants and very young children, where they can trigger laryngospasm or reflex apnoea, and concentrated oils should be kept out of reach and never taken neat.

The interaction profile is the second load-bearing point. Cineole is a substrate of CYP3A and an inducer of hepatic drug-metabolising cytochrome P450s ^{11,12,13Reference 11Miyazawa M et al. · 2001AnimalOxidation of 1,8-cineole, the monoterpene cyclic ether originated from Eucalyptus polybractea, by cytochrome P450 3A enzymes in rat and human liver microsomesView study →Reference 12Jori A et al. · 1972On the inducing activity of eucalyptol — animal studyView study →Reference 13Madyastha KM · 1986AnimalMetabolism of 1,8-cineole in rat: its effects on liver and lung microsomal cytochrome P-450 systems — animal studyView study →}; mechanistically this means cineole (or cineole-rich preparations taken regularly) could lower plasma levels of drugs cleared by these enzymes, though human interaction data are limited and the effect has not been quantified clinically. No formal maximum tolerated dose of the isolate is established beyond the trial ceiling of ~600 mg/day. Reproductive and developmental toxicity of isolated cineole in humans has not been well characterised; this is a scope limitation, not an all-clear.

Dosage

Across the double-blind trials the studied regimen is consistent: 200 mg of cineole three times daily (gut-soluble capsules), given as add-on therapy in COPD and asthma ^{1,2,3Reference 1Worth H et al. · 2009RCTConcomitant therapy with Cineole (Eucalyptole) reduces exacerbations in COPD: a placebo-controlled double-blind trial — randomised controlled trialView study →Reference 2Juergens UR et al. · 2003RCTAnti-inflammatory activity of 1.8-cineol (eucalyptol) in bronchial asthma: a double-blind placebo-controlled trial — randomised controlled trialView study →Reference 3Worth H · 2012RCTPatients with asthma benefit from concomitant therapy with cineole: a placebo-controlled, double-blind trial — randomised controlled trialView study →} and as monotherapy in acute bronchitis ^{5Reference 5Fischer J · 2013RCTEfficacy of cineole in patients suffering from acute bronchitis: a placebo-controlled double-blind trial — randomised controlled trialView study →}; the rhinosinusitis trial used 100 mg twice per capsule intake, three times daily (≈600 mg/day) ^{4Reference 4Kehrl W et al. · 2004RCTTherapy for acute nonpurulent rhinosinusitis with cineole: results of a double-blind, randomized, placebo-controlled trial — randomised controlled trialView study →}.

These are doses studied in research and are not a personal recommendation — appropriateness depends on the individual, their other medications (see the CYP interactions above) and professional guidance; concentrated eucalyptus/cineole oils are not a substitute for the standardised capsules and carry the ingestion hazards described above.

References