Hou Po Hua
StarMagnolia officinalis Rehd. et Wils.
Traditionally used for
- Nose & throat
- Digestion
☯ TCM Properties
Regulates Qi and Broadens the Middle Burner; Vents Constraint and Transforms Dampness; Aromatically Transforms Dampness; Harmonizes the Stomach
Traditional Chinese Uses
Hou Po Hua (magnolia flower bud) is warm, aromatic, and carries the same Qi-moving and Damp-drying properties as the magnolia bark (Hou Po) but with a lighter, more gentle action. It relieves Stomach and Spleen Qi stagnation with abdominal fullness and poor appetite, moves chest Qi stagnation for tightness and discomfort, and opens the orifices for nasal congestion. As the bud rather than the bark, its action is gentler and especially appropriate for the upper digestive tract and chest.
Western Herbalism Properties
Relationships
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Botanical Description
Magnolia officinalis Rehd. et Wils. (Magnoliaceae) is a deciduous tree 8-20 m tall with a stout trunk, smooth grey bark, and large, obovate to oblong-obovate leaves 20-45 cm long clustered toward the ends of the branches. In late spring, large, fragrant, solitary, cup-shaped flowers 10-15 cm across open at the branch tips; the nine to twelve fleshy white tepals surround numerous spirally arranged stamens and a conical aggregate of carpels that later develops into a reddish-brown, cone-like aggregate of follicles releasing bright orange-red, arillate seeds. Native to the mountains of central and eastern China and long cultivated, the dried flower buds (Hou Po Hua) are harvested before opening and used in TCM as a milder, more aromatic counterpart to the bark to regulate qi, harmonize the middle burner, and resolve dampness.
Active Constituents
Magnolol
Biphenyl neolignanConcentration: the Chinese Pharmacopoeia requires magnolol plus honokiol combined to be not less than 0.20% in the flower bud, against not less than 2.0% in the bark
Magnolol is a positive allosteric modulator of GABA-A receptors acting at the benzodiazepine site. In mice it shortens sleep latency and increases both non-REM and REM sleep at 5 and 25 mg/kg, prolongs pentobarbital sleeping time, and has anticonvulsant activity through the GABA/benzodiazepine receptor complex. The tenfold lower pharmacopoeial limit in the flower bud is the quantitative basis for Hou Po Hua being the milder, less drying drug compared with Hou Po bark.
Honokiol
Biphenyl neolignanConcentration: assayed jointly with magnolol; combined minimum 0.20% of the dried flower bud under the Chinese Pharmacopoeia
Honokiol, an isomer of magnolol, is likewise a positive allosteric modulator of both synaptic and extrasynaptic GABA-A receptors. It also antagonises the platelet collagen receptor glycoprotein VI and inhibits several cytochrome P450 isoforms in human liver microsomes, so it carries most of the drug's interaction liability.
beta-Eudesmol
Sesquiterpene alcoholConcentration: the drug's volatile oil is around 1%, of which 94 to 98% is alpha-, beta- and gamma-eudesmol, chiefly beta-eudesmol
Beta-eudesmol dominates the essential oil and carries most of the aromatic, damp-transforming character that makes the flower bud a Middle Burner drug rather than simply a weaker bark. The flower is used precisely for this fraction rather than for the neolignans.
Magnocurarine
Quaternary benzylisoquinoline alkaloidConcentration: under 0.1% in most commercial Magnolia bark samples; the alkaloid fraction as a whole is around 1% of the bark
Magnocurarine is N-methylcoclaurine methyl hydroxide, structurally half of a d-tubocurarine molecule, and it has a genuine curare-like neuromuscular blocking action; it was investigated in Japan as a candidate muscle relaxant. It was isolated from Magnolia obovata, and levels in Magnolia officinalis are low, but the alkaloid is the reason old sources caution against high-dose or long-term Magnolia bark use.
Magnoflorine
Aporphine alkaloidOne of the benzylisoquinoline-derived alkaloids identified in Magnolia officinalis bark alongside magnocurarine and salicifoline. It is a very widely distributed alkaloid and is not a useful identity marker for this species.
alpha-Pinene
Monoterpene hydrocarbonA minor but consistent component of the volatile oil, contributing to the aromatic profile on which the flower's traditional use for chest oppression and damp obstruction rests.
⚠ Drug Interactions
Benzodiazepines, Z-drugs, barbiturates, opioids and alcohol
Magnolol and honokiol are both positive allosteric modulators of synaptic and extrasynaptic GABA-A receptors, demonstrated by direct electrophysiology in recombinant and native receptors. Magnolol acts specifically at the benzodiazepine site: in mice it shortens sleep latency and increases non-REM and REM sleep at 5 and 25 mg/kg, prolongs pentobarbital sleeping time, and its antiepileptic effect is mediated through the GABA/benzodiazepine receptor complex. This is the same molecular target the prescribed hypnotic is acting on, so the effect is additive rather than merely coincidental. The flower bud carries these neolignans at roughly a tenth of the bark's assayed level, so the magnitude is smaller than for Hou Po itself, but the direction is identical and formulas often contain both the bark and other sedating herbs.
Clinical note: Take a full sedative and analgesic history before prescribing. Warn about driving and machinery in the first week, and be more cautious in the elderly and in anyone on an opioid. If the patient is on a benzodiazepine, do not change their dose without involving the prescriber.
CYP1A2 substrates (theophylline, clozapine, olanzapine, tizanidine, caffeine)
In human liver microsomes honokiol strongly inhibits CYP1A2 with IC50 values of 2.1 to 4.7 micromolar, and moderately to strongly inhibits CYP2B6, 2C8, 2C9 and 2C19 with IC50 values of 3.9 to 40.8 micromolar; honokiol also inhibits UGT1A9. Magnolol inhibits CYP1A2, 2B6 and 2C9 with IC50 values of 5.4 to 44.9 micromolar in human microsomes. The Planta Medica safety review notes that magnolol and honokiol are subject to glucuronidation and that interaction with pharmaceutical active principles cannot be excluded, although intervention trials of concentrated bark extract up to a year did not report adverse effects. Whether these microsomal IC50 values are reached in plasma from a decoction dose of the flower bud has not been established.
Clinical note: The concern is real but unquantified for whole-drug dosing. Be cautious with narrow-therapeutic-index CYP1A2 substrates, particularly theophylline and clozapine, and note that smoking status also swings CYP1A2 activity. Concentrated standardised magnolia bark extracts are the higher-risk exposure, not the flower bud in a decoction.
Warfarin, direct oral anticoagulants, aspirin and clopidogrel
Magnolol and honokiol were identified as the two antiplatelet agents of Magnolia officinalis: both inhibit aggregation and ATP release in rabbit platelet-rich plasma induced by collagen and arachidonic acid, without affecting ADP-, PAF- or thrombin-induced aggregation, and both inhibit thromboxane B2 formation and intracellular calcium mobilisation. Honokiol has since been characterised as a specific antagonist of the platelet collagen receptor glycoprotein VI, with ex vivo and in vivo human platelet data. Honokiol also inhibits CYP2C9, the enzyme clearing S-warfarin, which adds a second, pharmacokinetic route to the same outcome.
Clinical note: Ask about bruising, gum bleeding and epistaxis at follow-up. Stop the herb one to two weeks before elective surgery or dental extraction, and monitor INR more closely for the first month if the patient is warfarinised.
Non-depolarising neuromuscular blocking agents (rocuronium, vecuronium)
Magnocurarine, present in Magnolia bark, is N-methylcoclaurine methyl hydroxide and resembles one half of the d-tubocurarine molecule; it has documented curare-like action and was studied as a muscle relaxant candidate. However, it was isolated from Magnolia obovata, and in Magnolia officinalis it sits below 0.1% in most commercial samples with the whole alkaloid fraction around 1%. No case of clinically relevant neuromuscular interaction from Magnolia has been reported, and no data exist for the flower bud at all.
Clinical note: Not a reason to withhold the herb, but include it when listing herbal products to an anaesthetist. The general advice to stop herbal medicines two weeks preoperatively covers this alongside the stronger antiplatelet concern.
Xin Yi (Magnolia biondii, M. denudata, M. sprengeri flower bud) and Magnolia obovata bark
Two separate confusions matter here. First, Xin Yi is also a Magnolia flower bud, but from M. biondii, M. denudata or M. sprengeri, and it is a warm acrid exterior-releasing drug for nasal congestion, not a Middle Burner qi regulator; the names and the appearance are close enough that a careless substitution changes the prescription's whole direction. Second, commercial magnolia bark extract on the international supplement market is sourced from either M. officinalis or M. obovata and the two are frequently not distinguished on labels. This matters because magnocurarine, the curare-like alkaloid, was isolated from M. obovata, so a product labelled only Magnolia bark may carry a materially different alkaloid profile from the Chinese Pharmacopoeia drug.
Clinical note: Confirm you are receiving Flos Magnoliae Officinalis and not Flos Magnoliae (Xin Yi). For any concentrated extract product, require the binomial on the certificate of analysis, not just the word Magnolia.
Dosage
| Form | Amount | Frequency | Duration | Population | Notes |
|---|---|---|---|---|---|
| decoction | 3–9 g | Daily | — | — | 中国药典 2020 【用法与用量】3～9g。 【性味与归经】苦，微温。归脾、胃经。 — Chinese Pharmacopoeia 2020, quoted verbatim; route and cautions preserved. Replaces a cleared category-filler value. |
Evidence Tier
Moderate evidence · 4 studiesRecorded studies by study design, strongest design at the top. This is a study-design tier only, not a GRADE rating: it does not weigh risk of bias, consistency or precision.
Systematic review / meta-analysis
0
Randomized controlled trial
1
1 verified · 0 unverified
Other clinical trial
0
Observational / case report
0
In vitro / animal
3
1 verified · 2 unverified
Show 3 studies
- The natural products magnolol and honokiol are positive allosteric modulators of both synaptic and extra-synaptic GABAA receptors
- Magnolol, a major bioactive constituent of the bark of Magnolia officinalis, induces sleep via the benzodiazepine site of GABAA receptor in mice
- Effect of Honokiol on Cytochrome P450 and UDP-Glucuronosyltransferase Enzyme Activities in Human Liver Microsomes
Other / unclassified
0
Verified: design read from PubMed for a DOI that resolves to the cited paper Unverified: taken from the study's recorded description
Clinical Studies
The natural products magnolol and honokiol are positive allosteric modulators of both synaptic and extra-synaptic GABAA receptors
Electrophysiological characterisation showing that both magnolol and honokiol potentiate GABA-evoked currents at synaptic and extrasynaptic GABA-A receptor subtypes. This is the mechanistic basis for expecting additive sedation with benzodiazepines and other GABAergic drugs rather than an inference from behavioural data alone.
Magnolol, a major bioactive constituent of the bark of Magnolia officinalis, induces sleep via the benzodiazepine site of GABAA receptor in mice
Magnolol at 5 or 25 mg/kg significantly shortened sleep latency and increased both non-REM and REM sleep over the three hours after dosing in mice, with the effect localised to the benzodiazepine site of the GABA-A receptor. The study describes the constituent as isolated from Magnolia officinalis bark, not from the flower bud.
Effect of Honokiol on Cytochrome P450 and UDP-Glucuronosyltransferase Enzyme Activities in Human Liver Microsomes
Honokiol strongly inhibited CYP1A2 in human liver microsomes with IC50 values of 2.1 to 4.7 micromolar, and moderately to strongly inhibited CYP2B6, 2C8, 2C9 and 2C19 (IC50 3.9 to 40.8 micromolar). It also inhibited UGT1A9. These are the quantitative in vitro values behind the CYP1A2 substrate caution.
Effect of a proprietary Magnolia and Phellodendronextract on stress levels in healthy women: a pilot, double-blind, placebo-controlled clinical trial
Healthy premenopausal women aged 20 to 50 took 250 mg capsules of a proprietary Magnolia officinalis plus Phellodendron amurense bark extract or matched placebo three times daily for six weeks. Transient state anxiety on the Spielberger STATE questionnaire fell significantly versus placebo, but salivary cortisol and amylase, appetite, body morphology and sleep quality and latency did not change. Note carefully that this trial used a proprietary bark extract combined with a second herb, not Hou Po Hua, so it does not establish efficacy for the flower bud.
Historical Texts
Shen Nong Ben Cao Jing
Han dynastyYin Pian Xin Can
Republican periodPharmacopoeia of the People's Republic of China
Modern, 1963 edition onwardReferences
- Poivre M, Duez P. Biological activity and toxicity of the Chinese herb Magnolia officinalis Rehder & E. Wilson (Houpo) and its constituents . Journal of Zhejiang University-SCIENCE B (2017) [DOI]
- Sarrica A, Kirika N, Romeo M, Salmona M, Diomede L. Safety and Toxicology of Magnolol and Honokiol . Planta Medica (2018) [DOI]
This information is for educational purposes only and is not intended to replace professional medical advice. Always consult a qualified healthcare provider before using any herbal remedy, especially if you are pregnant, nursing, or taking medications.
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