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Indigo naturalis: Evidence for Ulcerative Colitis and Psoriasis, Practical Use, Dosage, and Risks

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Indigo naturalis—also known as Qing Dai—is a traditional blue pigment prepared from several plants, most commonly Baphicacanthus cusia, Polygonum tinctorium, and Isatis tinctoria. In East Asian medicine, finely milled powder or extracts have long been applied to stubborn skin conditions and, more recently, studied for ulcerative colitis. Modern research points to active constituents such as indigo, indirubin, and tryptanthrin that act on the aryl hydrocarbon receptor (AhR), a pathway involved in mucosal defense and inflammation resolution. Early clinical trials suggest benefit for moderate ulcerative colitis and for plaque psoriasis when used topically. At the same time, important safety signals—most notably rare cases of pulmonary arterial hypertension and liver enzyme elevations—mean indigo naturalis must be approached carefully. This guide distills how it works, who may benefit, how people use it, dosing ranges explored in studies, and the side effects and red flags you should know before considering it.

Essential Insights

  • Oral indigo naturalis (0.5–2.0 g/day for 8 weeks) improved clinical response in moderate ulcerative colitis in a randomized trial.
  • Topical preparations (ointments and oils) can reduce plaque psoriasis severity in small randomized studies.
  • Safety caveat: rare but serious pulmonary arterial hypertension has been reported; monitor for dyspnea, chest pain, or exercise intolerance.
  • Typical studied ranges: oral 0.5–2.0 g/day; topical twice daily thin layer to plaques or nails for 4–12 weeks.
  • Avoid if pregnant or breastfeeding, if you have pulmonary hypertension, significant liver disease, or are on hepatotoxic or QT-prolonging medications without specialist oversight.

Table of Contents

What is indigo naturalis?

Indigo naturalis is a dark blue powder produced by fermenting and processing the leaves or stems of indigo-yielding plants. While it is famous as a textile dye, the medicinal preparation is standardized for medical use and differs from crude dye pastes. The powder contains a mixture of bioactive molecules—chiefly indigo, indirubin, and tryptanthrin—along with plant-derived pigments and trace alkaloids. These compounds interact with the aryl hydrocarbon receptor (AhR), a cellular sensor that helps regulate immune tone, epithelial repair, and barrier function in skin and gut tissues.

Traditional practitioners employ indigo naturalis externally for scaly, thickened plaques on the skin and under the nails, and internally for inflamed mucosal surfaces in the digestive tract. In modern clinics, it is most often used:

  • Topically as an ointment, oil (sometimes called “Lindioil”), or compounded cream for plaque psoriasis and psoriatic nail changes.
  • Orally as capsules or fine powder for active ulcerative colitis, typically as an add-on to standard therapies.

Chemistry and sourcing matter. “Qing Dai” products may be derived from different plant species and extraction methods, leading to variability in indigo/indirubin content and in tolerability. Pharmaceutical-grade products undergo identity checks, specification testing (e.g., heavy metals, microbial limits), and controlled extraction. Non-standardized products can vary widely and may include contaminants or different plant species. Because benefit appears to track with both dose and constituent profile, reliable sourcing is not a luxury; it is a safety requirement.

Mechanistically, several actions help explain reported benefits:

  • AhR activation → IL-22 signaling: supports epithelial repair and tight junction integrity in the gut and skin.
  • Anti-inflammatory effects: indirubin modulates JAK/STAT and other pro-inflammatory pathways; tryptanthrin shows antimicrobial and anti-inflammatory activity in models.
  • Keratocyte and keratinocyte normalization: relevant to psoriatic plaques and nails, where abnormal proliferation and differentiation drive symptoms.

All of these point to the same practical idea: indigo naturalis is not an antiseptic or simple astringent—it is a bioactive mixture that nudges immune–epithelial crosstalk back toward balance. That promise must be weighed against known safety signals and the need for medical supervision when used by mouth.

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Does it work and key benefits

Ulcerative colitis (oral use): A multicenter, double-blind, placebo-controlled trial in adults with moderate disease tested daily doses of 0.5 g, 1.0 g, and 2.0 g for 8 weeks. Clinical response and mucosal healing rates improved in a dose-responsive manner compared with placebo. Many participants experienced decreased rectal bleeding and urgency, and endoscopic appearance often improved. Several follow-up cohorts report sustained benefit over months in clinical practice; however, these were uncontrolled, and the original randomized trial was stopped early after safety alerts elsewhere, underscoring the dual story of efficacy and risk.

Psoriasis (topical use): Small randomized studies demonstrate that indigo-based ointments and oils can reduce plaque thickness, scaling, and redness, with some nail studies showing improvements in discoloration and subungual hyperkeratosis. In mechanistic work, treatment lowered IL-17 pathway activity and normalized keratinocyte behavior, consistent with clinical response.

Symptom domains most likely to improve:

  • For ulcerative colitis: stool frequency, rectal bleeding, and endoscopic signs of mucosal inflammation, especially when used as add-on therapy in moderate activity.
  • For plaque psoriasis: plaque thickness and scaling; with oils and nail-friendly vehicles, nail surface irregularities can also improve.

Who tends to benefit most: Adults with moderate ulcerative colitis who have access to careful monitoring and who have either failed or cannot tolerate other options may see meaningful improvement during an 8-week induction. For psoriasis, individuals with localized plaques or nail involvement who prefer topical strategies may benefit, particularly when conventional topicals alone are insufficient.

What it does not do: Indigo naturalis is not a cure for inflammatory bowel disease or psoriasis. Relapses are common after discontinuation; some patients lose response over time. It should not be used as monotherapy in severe colitis, where rapid escalation to guideline-directed treatment is crucial, nor should it replace phototherapy or systemic agents when those are indicated for extensive psoriasis.

Benefit–risk lens: In settings with close medical supervision, short-term oral use can induce clinical response. But rare serious adverse events—most notably pulmonary arterial hypertension—require screening and clear stop rules. For psoriasis, topical use has a wider safety margin, though staining, irritation, and messiness are common. Across indications, the strongest results come from standardized products in well-defined regimens, not improvised preparations.

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How to use it practically

Form matters: Indigo naturalis appears in several forms—powder (for encapsulation), tablets/capsules, ointments, and oils. For internal use, capsules standardize intake. For skin and nails, ointments or indigo-in-oil preparations improve penetration and patient adherence.

Practical steps for oral use (ulcerative colitis), under clinician supervision:

  1. Baseline assessment: document disease activity, medication list, liver enzymes, and cardiopulmonary history; exclude pulmonary hypertension risk.
  2. Choose a standardized product: verify manufacturer quality controls and batch specifications (indigo/indirubin content, contaminants).
  3. Define an 8-week induction plan: agree on dose (see next section), adherence plan, and monitoring: symptoms weekly, labs by week 4–8, and an early stop rule for adverse effects.
  4. Add, do not swap: continue guideline-directed therapy unless your physician instructs otherwise; this reduces flare risk and clarifies add-on effect.
  5. Set exit criteria: if no clinically meaningful response by week 8 or if adverse signals emerge, discontinue and review alternatives.

Practical steps for topical use (psoriasis):

  1. Select vehicle: ointment for thick plaques; oil for nails and cosmetically sensitive areas.
  2. Apply thinly twice daily: massage into plaques or nail folds; avoid mucosal surfaces and broken skin.
  3. Mitigate mess: use dark clothing or bandage covers—staining is common.
  4. Reassess at 4–8 weeks: continue if improving and well-tolerated; pause if irritation, folliculitis, or staining is unacceptable.

What to combine—and what to avoid:

  • Compatible: oral use with mesalamine, some immunomodulators, or biologics (per physician plan); topicals with emollients or vitamin D analogues for psoriasis.
  • Use caution: concurrent hepatotoxic drugs, strong CYP modulators, or QT-prolonging agents; layering multiple astringent or keratolytic topicals that can irritate skin.
  • Avoid DIY extracts: artisanal preparations vary widely in strength and purity, raising safety and efficacy uncertainties.

Monitoring that prevents trouble:

  • Oral use: symptom diary; liver panel at baseline and during induction; prompt evaluation for chest pain, new shortness of breath, syncope, or unexplained fatigue.
  • Topical use: watch for contact dermatitis or folliculitis; discontinue if significant irritation occurs.

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Dosage: how much and when

Ulcerative colitis (oral): In the principal randomized trial, adults took 0.5 g, 1.0 g, or 2.0 g per day for 8 weeks, with higher doses yielding higher response rates. Many clinicians who use indigo naturalis as add-on therapy begin at 0.5–1.0 g/day and reserve 2.0 g/day for individuals without adequate response, provided safety monitoring is in place. Because the trial was stopped early after external safety alerts, most protocols limit oral use to defined induction windows, followed by reassessment or de-escalation.

Maintenance after response: Observational cohorts suggest some patients maintain remission with continued low-dose use; others lose response or experience adverse effects. There is no consensus maintenance dose. The conservative approach is to stop after 8 weeks, then monitor and decide on maintenance within standard care pathways. If continued, schedule regular safety checks (symptoms, liver enzymes; cardiopulmonary evaluation if indicated).

Psoriasis (topical):

  • Plaques: thin layer of indigo ointment twice daily to affected areas for 8–12 weeks, then taper to the lowest effective frequency.
  • Nails: indigo-in-oil preparations twice daily for 8–12 weeks targeting nail folds and subungual spaces; results may lag behind skin response.

Who should start lower—or not at all:

  • Start low (or avoid oral therapy altogether) if you have sensitivities to herbal products, are on multiple hepatotoxic medications, or have a history suggestive of pulmonary hypertension.
  • Do not initiate during pregnancy or while breastfeeding; avoid in children and in adults with advanced liver disease unless a specialist directs otherwise.

Timing and administration tips:

  • Take capsules with food to reduce nausea.
  • Separate oral dosing by at least 2–3 hours from iron or other cation supplements to reduce binding and absorption issues.
  • For topicals, gentle pre-soak or keratolytic pre-treatment (as advised by your dermatologist) can improve penetration into thick plaques.

Clear stop rules: discontinue immediately and seek medical care if you develop new or worsening shortness of breath, chest pain, unexplained dizziness, jaundice, dark urine, or persistent nausea.

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Risks, side effects, and interactions

Pulmonary arterial hypertension (PAH): Rare cases of PAH have been linked to prolonged oral use of indigo naturalis in ulcerative colitis. Some cases improved after discontinuation and appropriate therapy, but the potential severity makes this a critical warning. Typical presenting symptoms include exertional shortness of breath, chest discomfort, dizziness or syncope, and reduced exercise capacity. Individuals with prior pulmonary hypertension, connective tissue disease, congenital heart disease, or significant cardiopulmonary symptoms should not use indigo naturalis orally outside specialist care.

Hepatic effects: Mild, reversible elevations of liver enzymes were observed in trials. People with chronic liver disease, heavy alcohol use, or concurrent hepatotoxic drugs (e.g., high-dose acetaminophen regimens, certain antitubercular or antiepileptic medications) face higher risk and should avoid oral indigo naturalis unless a physician advises otherwise and monitors closely.

Gastrointestinal: Nausea, abdominal discomfort, and constipation are occasionally reported with oral use; these often improve with food or dose adjustments but should not be ignored if persistent.

Dermatologic (topical): Local irritation, folliculitis, and blue staining of skin, nails, clothing, and bedding are common annoyances. Reduce frequency, adjust vehicle, or pause therapy if irritation occurs.

Laboratory interference: Deep blue pigments may stain stool or skin and can alarm patients; this is cosmetic. No consistent interference with standard lab assays is reported, but inform your care team about current treatments.

Drug interactions and precautions:

  • Hepatotoxic agents: additive risk; avoid combinations where possible.
  • Drugs with narrow therapeutic windows: while specific enzyme interactions are not well defined, use extra caution and involve a pharmacist when combining with agents like warfarin, tacrolimus, or certain antiarrhythmics.
  • AhR-active compounds: theoretical pathway overlap exists (dietary crucifers, smoke constituents), but clinical significance is unclear.

Who should avoid indigo naturalis:

  • Pregnancy or breastfeeding.
  • Children without specialist oversight.
  • History of pulmonary hypertension or unexplained exertional dyspnea.
  • Significant liver disease or prior herb-induced liver injury.
  • Inability to access monitoring (no follow-up, no labs).

When to seek immediate care: new shortness of breath, chest pain, fainting, swelling of legs, yellowing of the skin or eyes, very dark urine, fever with severe abdominal pain, or bloody diarrhea.

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Evidence summary and research

Ulcerative colitis: A pivotal multicenter randomized trial demonstrated that 0.5–2.0 g/day for 8 weeks can induce clinical response and improve endoscopic healing in moderate disease. Observational cohorts over 6–12 months show continued benefit for some, but heterogeneity in products and dosing—and the early stoppage of the pivotal trial after external safety alerts—limit certainty about long-term use. A growing 2024 review synthesizes efficacy and safety across studies and emphasizes careful patient selection, short induction courses, and vigilance for cardiopulmonary symptoms.

Psoriasis (skin and nails): Multiple controlled studies, including randomized, vehicle-controlled designs and mechanistic trials, show reductions in plaque severity and nail involvement with topical indigo formulations. Mechanistic work indicates down-regulation of IL-17–related signaling and normalization of keratinocyte proliferation, consistent with clinical improvements. Benefits are generally modest to moderate and depend on adherence; staining remains the primary barrier.

Mechanism of action: Indigo, indirubin, and tryptanthrin collectively act at AhR, shifting epithelial–immune signaling toward barrier repair and inflammation resolution, with downstream effects on IL-22 and related pathways. This mechanism plausibly explains improvements in both mucosal colitis and psoriatic plaques.

Safety signals: Case reports and case series link prolonged oral use to pulmonary arterial hypertension, with some reversibility after stopping therapy. Mild liver enzyme elevations are seen in trials. The balance of benefit and risk favors short, supervised induction for select UC patients, and topical use for psoriasis.

Research gaps and priorities:

  • Standardization: define robust constituent specifications (e.g., indigo/indirubin ratio) and batch quality controls tied to outcomes and safety.
  • Dose–response and maintenance: clarify optimal induction dosing, whether maintenance is useful or harmful, and how to de-escalate safely.
  • Biomarkers for risk: identify predictors of PAH susceptibility and early detection during therapy.
  • Comparative effectiveness: determine how indigo naturalis fits alongside biologics, small molecules, and advanced topicals.

Until those data arrive, indigo naturalis should be positioned as an adjunct—not a replacement—for guideline-directed care, with clear protocols, limited duration, and fast response to adverse signals.

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References

Disclaimer

This content is educational and does not replace personalized medical advice, diagnosis, or treatment. Do not start or stop any medication or supplement without guidance from a qualified clinician who knows your medical history. Indigo naturalis can cause rare but serious side effects, including pulmonary arterial hypertension and liver enzyme elevations. Avoid during pregnancy and breastfeeding, in children without specialist oversight, and in people with pulmonary hypertension or significant liver disease. If you experience chest pain, new shortness of breath, fainting, yellowing of the skin or eyes, or severe abdominal symptoms, stop the product and seek urgent medical care. If you found this guide useful, please consider sharing it on Facebook, X (formerly Twitter), or your preferred platform, and follow us for future evidence-based updates. Your support helps us continue producing high-quality health content.

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