What Is Indigo Naturalis and How Does It Work?

Indigo naturalis, also sold as Qing Dai, is a traditional Chinese medicine made from the same plants that once gave the world blue dye. It has drawn modern attention because some people with stubborn ulcerative colitis and psoriasis improve on it when standard treatments have failed.¹ It is not a gentle herbal tonic, though. It acts on the body strongly enough to cause rare but serious harm when swallowed,² so whether it is worth trying depends as much on its risks and monitoring as on how well it works.

Where Indigo Naturalis Comes From

Indigo naturalis is a dried powder made from several indigo plants, including Strobilanthes cusia, Persicaria tinctoria and Isatis tinctoria.³ In Chinese it is called Qing Dai, the name you will often see on supplement labels and in gut-health research. In China it has been used for thousands of years for nosebleeds, coughing up blood, mouth ulcers and childhood convulsions.⁴ Today’s interest centers on bowel inflammation and psoriasis, and tradition alone doesn’t show that it works for these newer purposes.

The same blue pigment, indigo, was historically the dye behind denim and other textiles.⁵ The medicine is a crude whole-plant powder containing many compounds besides indigo, not a single pure chemical. Modern synthetic indigo made for dyeing textiles is a different product and should never be swallowed or applied as a stand-in.

The powder is made by soaking plant material and adding lime, a process that varies by maker.⁶ So its quality shifts with plant source, lime amount, soaking time, climate and season.⁷ Its main active ingredients are indigo, indirubin and tryptanthrin.⁸

Does Indigo Naturalis Work for Ulcerative Colitis

Ulcerative colitis is long-term inflammation and ulcers in the lining of the large bowel, causing bloody diarrhea and urgency. In a multicenter trial, 55% of people taking 1 gram a day were in remission at 8 weeks, versus under 5% on placebo.⁹ The 2 gram dose did less well, with 38% in remission, so more is not clearly better.¹⁰ In another short trial, about 83% improved on indigo naturalis versus 26% on placebo.¹¹

The terms matter for daily life. Response means symptoms have clearly eased, such as fewer bathroom trips or less bleeding, though some may remain. Remission means symptoms are largely gone, with near-normal stools and no visible blood. Doctors usually judge this from your symptoms and blood tests, and sometimes from a scope that looks at the bowel lining. In the trials, these improvements were measured at about 8 weeks.

Results held up over longer periods in practice. In a one-year real-world study, about 73% of patients were in remission at 52 weeks.¹² It has helped some people whose colitis resisted standard drugs.¹³ A 6-week course also brought remission in children with mild to moderate colitis, in an open trial without a comparison group.¹⁴

There are limits to how far this can be trusted. Most of the trials were small and short, so they cannot rule out rarer problems or show how results hold up in larger groups. Most were done in Japan and China, and results may not carry over exactly to people elsewhere. Evidence on long-term safety is thinner than evidence on short-term benefit, which matters given the risks described later. Indigo naturalis is not an approved standard colitis drug in most countries, so it sits outside usual treatment guidelines.

How Indigo Naturalis Works in the Body

Indigo attaches to a sensor in gut-lining cells.¹⁵ Once switched on, it changes which genes the cell uses, shifting the cell’s behavior toward repair and calmer signaling. In lab-grown cells, switching on this sensor helps lining cells grow and move to close sores.¹⁶

Swallowed indigo switched on this sensor in the colon but not the liver in animals, suggesting it acts from inside the bowel.¹⁷ In one patient group, a marker of this sensor rose more than 12,000-fold in the colon after 8 weeks.¹⁸ When the sensor was blocked in mice, the benefit disappeared.¹⁹

The sensor also seems to steer the immune system. Activating it appears to rebalance two immune cell types, one that fuels inflammation and one that restrains it.²⁰ In animals, its compounds lowered key inflammation messengers such as TNF-alpha and IL-6.²¹ In rats it raised butyrate, a gut-bacteria product that soothes the bowel lining.²²

The same sensor is found in skin cells, which helps explain why a powder studied for the gut may also help psoriasis. In lab and mouse studies, its compounds slowed overgrowing skin cells, cooled inflammation and reduced new blood vessels in psoriasis.²³

Most of this mechanism evidence comes from mice, rats and cells grown in dishes, not from people. Human trials show that it helps, but they do not confirm each step of how. So the mechanism is a working explanation rather than a settled account.

Indigo Naturalis Ointment for Psoriasis and Eczema

In one trial, 56% of people using the ointment cleared at least three-quarters of their psoriasis by 8 weeks, versus none on placebo.²⁴ Stronger ointments worked best, with the highest-strength group improving about 69% on average.²⁵ No serious treatment-related side effects appeared over 20 weeks.²⁶ A skin patch version worked about as well as a standard prescription psoriasis cream in 4 weeks.²⁷

The raw powder is intensely blue and can stain skin, nails and clothing. Expect to cover treated areas and protect bedding and clothes while using a blue ointment.

Nails responded too. An oil extract called Lindioil cut nail psoriasis scores by about half in 12 weeks, versus about a fifth with plain oil.²⁸ The same oil has been tested for eczema.²⁹ In one child with stubborn psoriasis, the ointment brought remission lasting over 2 years.³⁰

Applied to skin, the medicine is thought to mostly stay where it is put, rather than reaching the gut and bloodstream in the same way. The serious harms reported, such as lung blood-pressure problems and colon injury, came from taking it by mouth. The skin products in studies were made to measured strengths, unlike loose powders whose strength is unknown. Even so, skin use is better studied over weeks than over years, so a doctor’s oversight still makes sense.

Side Effects and Serious Risks of Taking It by Mouth

Common mild side effects include abnormal liver tests, headache, stomach or belly pain and nausea.³¹ Serious cases of acute liver damage have also been reported.³²

The most serious known risk is pulmonary arterial hypertension, which is high blood pressure in the lung arteries that strains the heart.³³ It has appeared in people taking Qing Dai for ulcerative colitis.³⁴ It may improve after the herb is stopped.³⁵ Breathlessness, tiredness or ankle swelling while taking it needs prompt medical attention.

It can also damage the bowel lining through reduced blood flow, which doctors call ischemic colitis.³⁶ In one large group taking indigo-containing patent medicines, about 1 in 77 developed this injury.³⁷ New sudden belly pain or more bleeding should be reported quickly.

This injury is easy to mistake for a colitis flare, since both cause belly pain and bloody stools. Improvement after stopping the herb can be a clue, since an injury caused by it tends to improve once it is stopped, but it is not proof on its own. A colonoscopy may be needed to look at the bowel lining and see which problem is present.

Careful monitoring has several parts. Regular blood tests check liver function, since abnormal results are among the common effects. At each visit the doctor should ask about breathlessness, tiredness and ankle swelling, the early signs of lung blood-pressure trouble. Some doctors also order a heart ultrasound to look for strain on the heart. Monitoring continues for as long as the herb is taken, not only at the start, because problems can appear later.

Product Quality and Contamination

Many commercial samples meet official standards yet contain too much lime, making them strongly alkaline.³⁸ Indigo naturalis was also rated a high risk for arsenic contamination among Chinese herbs.³⁹ Some formulas deliberately combine it with realgar, an arsenic mineral, for a blood cancer.⁴⁰ Adding indigo naturalis kept arsenic in the blood longer in mice.⁴¹ Trials used measured doses like 1 gram a day, while loose powders vary in strength.

Buy it only through a doctor or a supplier that publishes laboratory testing, since the label alone cannot show lime or arsenic content. Avoid mixed formulas unless a doctor prescribed them, because other ingredients add unknowns. Check whether realgar appears in the ingredient list. Tell your doctor exactly which product and brand you use so any problems can be traced.

Using Indigo Naturalis Safely

Discuss it with your gastroenterologist or dermatologist before starting. Don’t stop prescribed colitis medicines on your own to switch. For skin, a tested ointment is a lower-risk first option than swallowing powder. Children have used it in studies, but only under specialist care.⁴²

A few questions are worth bringing to the appointment. Ask which dose and which specific product they recommend, so you are not choosing one yourself. Ask how often blood tests and heart checks will happen while you take it. Ask which symptoms should make you stop and call right away. And ask how long a trial period should last and what result would mean it is time to stop.

Safety in pregnancy hasn’t been established. Tell your doctor about every herb and drug you take, and avoid combining indigo naturalis with other unregulated herbal mixes.