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Traditional Chinese medicine

Magnolia barkMagnolia officinalis

Magnolia bark (hou po) is the bark behind Ping Wei San and Da Cheng Qi Tang; we found no gut trial of it alone, only formula trials and a mouse ileus study.

Botanical name
Magnolia officinalis
Part used
stem and root bark, dried; often prepared with ginger
Also called
pinyin Hou po (厚朴); Houpu magnolia, Magnoliae officinalis cortex, Koboku (Japanese)
Used in
Traditional Chinese medicine
Taken for
Bloating, Indigestion, Constipation, Nausea
Sold as
decoction, granule extract, capsule extract, patent medicine, dried bark

The plant

Magnolia bark, or hou po, is the dried bark of Magnolia officinalis and its variety biloba, a tree. Magnolia obovata bark is used in Japanese traditional medicine, and a processed form of the Chinese bark, prepared with ginger (jiang hou po), is also used. Magnolia bark extract is a dietary supplement ingredient too, standardized to magnolol and honokiol, and the traditional uses reviewed in the literature include anxiety and depression as well as gut complaints.

In the digestive tradition, it is the herb for fullness and distention. It is in Ping Wei San (with atractylodes lancea, tangerine peel and licorice), in Huo Xiang Zheng Qi San, and in Da Cheng Qi Tang, where it is paired with rhubarb, mirabilite and immature bitter orange. Banxia Houpo Tang, in which it sits with pinellia, poria, perilla leaf and fresh ginger, is the Japanese Kampo formula hangekobokuto. Magnolia bark is taken as a decoction, a granule extract, in patent medicines and as capsule extracts.

How the traditions use it

Traditional Chinese medicine (about TCM)

Hou po is bitter, acrid and warm in the materia medica, entering the spleen, stomach, lung and large intestine channels, with the actions of moving qi, drying dampness, directing rebellious qi downward and relieving fullness. A Journal of Ethnopharmacology review of the bark lists its traditional uses as abdominal distention, vomiting, diarrhea, accumulation of food, qi stagnation, constipation, retained phlegm and cough from asthma. In Da Cheng Qi Tang it supports rhubarb by what the tradition calls moving qi to relieve distention; in Ping Wei San it helps cang zhu dry dampness in a stomach that feels full and heavy. Qi stagnation here is a pattern term from the texts and not an anatomical finding.

What is in it

The bark holds more than 200 compounds, according to a review in the Journal of Ethnopharmacology, including lignans, phenylethanoid glycosides, alkaloids, steroids and essential oils. Its best-known lignans are magnolol and honokiol, which laboratory work reports as having antioxidant, anti-inflammatory, antibiotic and antispasmodic effects. In a mouse model of postoperative ileus, a Kampo formula built on magnolia bark (hangekobokuto) cut infiltration of neutrophils and macrophages and restored delayed intestinal transit. These are cell and animal findings, not results in people, and a review of the bark notes that the mechanisms behind them have not been worked out.

What the human trials show

We could not find a controlled trial of magnolia bark on its own for a gut outcome. A review of the bark says that only a very few clinical trials of it have been published. The human gut data are trials of formulas that contain it.

The largest is for Da Cheng Qi Tang, the rhubarb, mirabilite, bitter orange and magnolia bark formula for what the tradition calls obstructed bowels. A meta-analysis of 60 trials with 6,095 people with intestinal obstruction found that adding it to conservative therapy raised the response rate (48 trials, 4,916 patients, RR 1.25, 95% CI 1.20 to 1.30) and shortened time to first flatus after abdominal surgery (11 trials, 1,040 patients, SMD -2.09). The formula alone was not significantly better than conservative therapy (6 trials, 361 patients, RR 1.13, 0.97 to 1.31). The effect stayed similar when trials at high risk of bias were excluded.

Huo Xiang Zheng Qi, which also contains magnolia bark, was tested against placebo in 212 adults with diarrhea-predominant IBS: the response-rate difference at 4 weeks was 0.29 (95% CI 0.14 to 0.43), and the IBS symptom severity score fell more (mean difference -10.92). The authors state that the oral liquid came from its manufacturer, which took no part in the analysis.

Not tested: magnolia bark or its lignans alone for any digestive symptom, and Ping Wei San in a randomized trial we could find.

StudyDoseWhat it found
Meta-analysis of 60 RCTs, 6,095 people with intestinal obstruction or postoperative ileus (Da Cheng Qi Tang, contains magnolia bark) PMID 25392589Decoction, alone or with conservative therapyAdd-on response RR 1.25 (1.20 to 1.30); time to first flatus SMD -2.09; alone, RR 1.13 (0.97 to 1.31), not significant
Multicenter double-blind RCT, 212 adults with IBS-D (Huo Xiang Zheng Qi oral liquid, contains magnolia bark) PMID 4129732120 ml twice a day for 4 weeksResponse-rate difference 0.29 (95% CI 0.14 to 0.43); IBS-SSS mean difference -10.92; no serious adverse events
Animal study: mouse model of postoperative ileus given hangekobokuto (not a human trial) PMID 36216552Oral, before and after bowel manipulationLess neutrophil and macrophage infiltration; delayed intestinal transit recovered
Review of Magnoliae officinalis cortex: botany, chemistry, pharmacology and toxicology PMID 30818008Not applicableMore than 200 compounds; effects on the digestive system reported in laboratory work

How much the studies and the texts used

No trial gives a dose of magnolia bark alone for the gut. The Huo Xiang Zheng Qi trial used 20 ml of oral liquid twice a day for 4 weeks. The traditional preparation is a water decoction of the bark, usually the ginger-prepared form, simmered with the other herbs of the formula and drunk in divided doses. Concentrated magnolia bark extract, standardized to magnolol and honokiol, is sold as a supplement with its own labeled dose, which is not derived from a gut trial.

Doses here describe what studies and pharmacopoeias used. They are not a recommendation for any person; a clinician or pharmacist who knows your medicines and conditions is the right person to ask.

Side effects and cautions

A toxicology review of magnolol and honokiol reports that concentrated magnolia bark extract was not mutagenic or genotoxic in laboratory tests, that a subchronic animal study established a no-adverse-effect level above 240 mg per kg a day, and that human intervention trials using the concentrated extract for up to a year reported no adverse effects. Those trials were not gut trials. The review discloses that two of its authors are employees of the confectionery company Perfetti Van Melle. No controlled data on pregnancy or breastfeeding turned up. On product quality, an overview of 26 systematic reviews of herbal products reported contamination and adulteration with heavy metals, pesticides and prescription drugs, noting contamination most often for Chinese remedies and adulteration most often for Indian ones; it makes no finding about magnolia bark.

Interactions

The toxicology review notes that magnolol and honokiol are cleared by glucuronidation, like other dietary polyphenols, and says an interaction with medicines or other herbal constituents cannot be excluded. No controlled interaction study of the bark in people turned up. The bark is also used for sedative effects, according to the toxicology review, and combination products may include licorice, rhubarb, ginger or ginseng, whose interaction notes apply to the finished formula.

Magnolia bark on the shelf: the products that contain it

The products here name magnolia bark among their actives. How much of it a serving holds, and whether that matches any trial, is on each page.

Snap Dynasty Stomach Chi 4.5 out of 5 from 162 ratings from Amazon · $1.50 per day at two capsules three times a day ($29.99 for 120 on the brand site, $29.98 on Amazon, a 20-day bottle); the 60-capsule bottle is $17.99 Health Concerns Quiet Digestion 4.5 out of 5 from 54 ratings from Amazon · $2.39 per day at two capsules three times a day ($35.90 for 90 on the brand site and Amazon, a 15-day bottle); the 270-capsule size is $1.89 a day

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Often paired or compared

TCM / Western Rhubarb root Rheum palmatum; Rheum officinale TCM Pinellia Pinellia ternata TCM Atractylodes Atractylodes macrocephala (bai zhu); A. lancea (cang zhu) TCM Agastache Agastache rugosa (the Chinese pharmacopoeial huo xiang is Pogostemon cablin) TCM Perilla Perilla frutescens

The questions that come up

What is magnolia bark used for in Chinese medicine?

The texts use hou po for abdominal fullness, distention, vomiting and constipation, which they attribute to qi that does not move. It is a component of Ping Wei San, Huo Xiang Zheng Qi San and Da Cheng Qi Tang.

Is the magnolia bark in supplements the same as hou po?

It is the same species, Magnolia officinalis, but supplements are concentrated extracts standardized to magnolol and honokiol, a different preparation from the sliced bark simmered in a decoction.

Is there human evidence for magnolia bark for digestion?

We could not find a controlled trial of the bark alone for a digestive symptom. Formula trials exist, including a 212-person IBS-D trial of Huo Xiang Zheng Qi and a 60-trial meta-analysis of Da Cheng Qi Tang for intestinal obstruction.

What are magnolol and honokiol?

They are the two best-known lignans in the bark. Laboratory work reports antispasmodic and anti-inflammatory effects, but their effect on the human gut has not been tested in trials we could find.

What is hangekobokuto?

It is the Kampo name for Banxia Houpo Tang, which combines magnolia bark with pinellia, poria, perilla leaf and ginger. In mice, it reduced inflammation and restored intestinal transit after bowel surgery.

Sources