Why is my poop green? Food, bile, iron and when to worry

The answer

Green poop usually comes from what you ate or took: the chlorophyll in spinach, kale and broccoli, green, blue or purple dye, iron pills, bismuth or some antibiotics. Stool that rushes through, as in diarrhea, can also stay green because bile has no time to turn brown. A food tint should clear within a day or two, a Cleveland Clinic gastroenterologist says.

In five lines

1 to 2 days: how long a green tint from food should last once the source has left your system, according to Cleveland Clinic gastroenterologist Christine Lee, MD. [Cleveland Clinic, 2026]
Green to brown: bile starts out yellowish-green, and stool that moves through too fast, as in diarrhea, can come out green because the bile had no time to change color. [Northwestern Medicine, 2025; Harvard Health, 2024]
3 medicines: iron supplements, bismuth subsalicylate and some antibiotics can all make stool greenish, Harvard Health says. [Harvard Health, 2024]
Several days: MedlinePlus says to contact a health care provider when stools are not the normal brown color for several days. [MedlinePlus]
Black, red, pale: the stool colors the sources send to a doctor, because black or tarry stool can mean bleeding high in the gut and pale or clay stool can mean a problem with bile flow. [MedlinePlus; NHS]

What does green poop mean?

Most of the time, something you ate. Harvard Health's chief medical editor writes that occasional green stool in someone who otherwise feels fine usually comes from dark green vegetables such as spinach and kale. Cleveland Clinic's Christine Lee, MD, puts the test in one line: "If you feel perfectly fine and don't have diarrhea, a different color bowel movement is most likely linked to something you ate."²¹

Harvard adds that a temporary change from the usual brown most often does not signal a serious problem.² The other causes fall into three groups: medicines that tint stool, stool that moves through too fast for bile to change color, and changes in how much bile reaches the gut. Each one is in the table below, with the source that names it. Shape and firmness are a separate question, covered type by type in our Bristol stool chart.

Why does poop turn green?

Either a green pigment passed through, or bile stayed green. Stool gets its usual brown from bile, a greenish-brown digestive fluid, Cleveland Clinic explains, and MedlinePlus says the liver releases bile salts into the stool, which gives it its normal brown color. Bile itself starts out yellowish-green, so anything that adds green or leaves bile unchanged shows up in the toilet.⁴⁵³

Causes of green poop, one by one

Cause	Why it turns stool green	What the source says to expect	Source
Leafy greens	Chlorophyll, the pigment in spinach, kale and broccoli	"The chlorophyll that gives those vegetables their green color can do the same to your poop." A food tint should clear within a day or two.	Cleveland Clinic¹; Northwestern Medicine³
Other green foods	Avocados, green apples, honeydew melon, herbs such as basil and parsley, matcha, pistachios and hemp seeds can tint stool green	Listed as possible green sources; the tint fades once the food has passed	Cleveland Clinic¹
Blue and purple foods	Pigments in blueberries, blackberries and other blue or purple produce	Can turn normal brown stool green for a short time	Northwestern Medicine³; Cleveland Clinic⁴
Food dye	Green dye, or blue and purple dye mixing with digestive juices	Stool returns to brown once the dye has left your system	Cleveland Clinic¹
Iron supplements	Iron darkens stool	Dark green or even blackish, Dr. Lee says; the NHS calls darker poo common with iron	Cleveland Clinic⁴; Northwestern Medicine³; NHS⁶
Bismuth subsalicylate	Reacts with sulfur in the digestive system	Stool may be dark green or even black	Northwestern Medicine³
Antacids with aluminum hydroxide	Named as a side effect, mechanism not given	Greenish poop	Northwestern Medicine³
Antibiotics	They change the gut's bacteria	A greenish, or sometimes yellow, tint	Cleveland Clinic¹⁴
Diarrhea or fast transit	Bile moves through before it can change from green to brown	Green, loose stools while it lasts	Harvard Health²; Northwestern Medicine³
A high-fat diet	The liver makes more bile to digest the fat	More green bile in stool, which can turn it bright green	Northwestern Medicine³
Gallbladder removal	Bile flows straight from the liver into the small intestine	A temporary color change; Cleveland Clinic adds greenish diarrhea	Northwestern Medicine³; Cleveland Clinic¹

Sources: Cleveland Clinic Health Essentials, Jan 8, 2026 and Feb 26, 2025; Northwestern Medicine HealthBeat, Feb 15, 2025; Harvard Health Publishing, Apr 1, 2024; NHS, ferrous sulfate side effects. All read on Oct 26, 2026. Brand names of the medicines are left out.

Can iron pills or antibiotics make your poop green?

Yes, both can. Harvard Health lists iron supplements, bismuth subsalicylate and some antibiotics among the medicines that can turn stool greenish, and Dr. Lee tells people who take iron not to be surprised if their stool turns dark green or even blackish. Antibiotics work through the gut's bacteria: they change its flora, which can add a greenish tint, Cleveland Clinic says.²⁴¹

The NHS guidance on iron tablets calls darker than usual poo a common side effect and "usually nothing to worry about." It draws the line clearly: talk to a doctor straight away if your poo is black, tar-like or red, or has blood in or on it. If a side effect keeps bothering you, its advice is to speak to a doctor or pharmacist.⁶

Why is diarrhea sometimes green?

Speed. Bile is a yellowish-green fluid made by the liver to help digest fat, and when it moves through the intestines too quickly, as it can with diarrhea, its color may not have time to change from green to brown, Northwestern Medicine gastroenterologist Olufemi Kassim, MD, explains. Harvard Health calls it the rapid passage of green bile from the small intestine.³²

A stomach bug can bring green, loose stools too: Cleveland Clinic lists bacterial and viral infections, and a gut parasite that sends unabsorbed bile through in a rapid gush. Dr. Lee adds a caution of her own: "All of these issues are possible, but they're not the norm."¹ Which fiber firms loose stools, what to eat and drink while they last, and the dehydration signs that need a doctor are set out in does fiber help with diarrhea?

Does fiber or eating more greens change your poop color?

Greens can; fiber changes speed and bulk rather than color. The green comes from chlorophyll in vegetables such as spinach, kale and broccoli, which Cleveland Clinic and Northwestern Medicine both name, so a large serving of leafy greens can tint the next stool. None of the sources we read says fiber on its own turns stool green.¹³

What fiber does change is pace. A 2015 review of 65 intervention studies in generally healthy people found that each extra gram of wheat fiber a day raised total stool weight by 3.7 g a day, and cut transit time by 0.78 hours in people whose transit started above 48 hours. A breakfast cereal company paid for that review.¹⁰ How many grams to aim for, by age and sex, is in how much fiber per day?

What color poop should worry you?

Black or tarry, red, and pale or clay-colored stool. MedlinePlus says black, tarry stool with a foul smell is a sign of a problem in the upper digestive tract, most often bleeding, while red or fresh blood most often points to bleeding lower down. Pale, clay or putty-colored stool can mean the liver is making less bile or its flow is blocked. Food and medicines can mimic some of these colors, as the table shows.⁷⁵

Stool colors the sources send to a doctor

Color	Harmless causes the sources name	What it can mean, per the source	What the source says to do
Black or tarry	Iron pills, black licorice, blueberries, activated charcoal, bismuth medicines⁷	Bleeding in the esophagus, stomach or first part of the small intestine⁷	Contact a provider right away if you notice blood or a change in stool color, vomit blood, or feel dizzy⁷; the NHS says black or dark red poo needs an urgent appointment⁸
Red	Beets, foods with red coloring⁷; tomatoes and beetroot⁸	Bleeding from the colon, rectum or anus⁷	Get help at once if the bleeding will not stop or there is a lot of blood, the NHS says⁸
Pale, clay or putty-colored	Some medicines⁵	Reduced bile, or bile blocked on its way out of the liver; yellow skin and dark urine can come with it⁵	Contact a provider if stools are not the normal brown color for several days⁵
Green	Greens, dyes, iron and the other causes above¹	Usually food; sometimes fast transit or a stomach bug¹²	Call a doctor if it lingers or comes with belly pain, bleeding, fever or vomiting¹

Sources: MedlinePlus, Black or tarry stools (reviewed Apr 27, 2026) and Stools, pale or clay-colored (reviewed Aug 12, 2024); NHS, Bleeding from the bottom (reviewed Apr 12, 2023); Cleveland Clinic. All read on Oct 26, 2026. A provider can test stool for blood when food or medicine could explain the color, MedlinePlus notes.

Babies follow different rules: Cleveland Clinic says healthy stool colors for babies vary with breast milk or formula, so a baby's stool questions belong with a pediatrician.⁹

When should you see a doctor about green poop?

When the green lasts or other symptoms come with it. Cleveland Clinic names belly pain, a drop in your weight that you did not plan, bleeding, fever and vomiting, and flags pale or blood-tinged stool too. Northwestern Medicine adds severe cramping, bloody or jet-black poop, severe and persistent diarrhea, and dehydration. Both say an occasional green stool on its own is usually harmless.¹³

Dr. Kassim's advice is to learn your own normal: "If you notice a sudden or lasting change in color, regardless of the color, and it's not related to your diet, talk to your doctor." Cleveland Clinic's health library makes the same point about time: contact a provider if your poop does not go back to brown within a few days.³⁹

In brief

Green poop is usually food or dye, sometimes iron, bismuth or an antibiotic, and sometimes stool that moved too fast for green bile to turn brown; a food tint clears in a day or two. Black or tarry, red, or pale stool, or green that lasts or comes with pain, fever, vomiting or bleeding, means a call to your doctor.

How we reported this

Reader questions: In a pull of 1,145 public Reddit posts (250 communities, Sep 12 to Oct 12, 2026), 79 talked about poop or stools, and none described green stool.
Search question: "Why is my poop green?" with its neighbors, "green poop" and "what does green poop mean," plus the follow-up AI assistants run on causes and when to worry.
Label facts: None. This page names no Physician's Choice product.
Sources: Ten public sources, each fetched and read on Oct 26, 2026: three Cleveland Clinic pages, Northwestern Medicine, Harvard Health, two MedlinePlus pages, two NHS pages and one review through PubMed Central. Brand names in the sources are left out.
House wording: None. No Physician's Choice wording is used on this page.

Stool color questions, answered

What does green poop mean?

Most often, something you ate: leafy greens, green, blue or purple dye, or blue foods such as blueberries. Iron pills, bismuth and some antibiotics can do it too, as can stool that moves so fast that green bile has no time to turn brown. If you feel well with no diarrhea, Cleveland Clinic says food is the likely cause.

Is green poop normal?

Now and then, yes. Harvard Health and Cleveland Clinic both say an occasional green stool in someone who feels well is usually harmless and often follows dark green vegetables. Brown is still the usual color. Green that lasts for days, or comes with pain, fever, vomiting or bleeding, is the point to call a doctor.

How long does green poop last?

If food or dye caused it, about a day or two once the source has passed through, Cleveland Clinic's Dr. Lee says. MedlinePlus advises contacting a health care provider when stools stay off their normal brown color for several days, and Cleveland Clinic's health library says the same of poop not back to brown within a few days.

Can iron pills make your poop green?

Yes. Harvard Health lists iron supplements among the medicines that can turn stool greenish, and Cleveland Clinic says iron can make stool dark green or even blackish. The NHS calls darker poo common with iron. Stool that is black, tar-like or red, or has blood in it, needs a doctor straight away.

Is dark green poop a sign of bleeding?

Not on its own, in the sources we read. The color they tie to bleeding high in the gut is black and tarry, often with a foul smell, and the one tied to bleeding lower down is red. Iron pills and bismuth can darken stool to dark green or black, so tell your doctor what you take.

Sources

Cleveland Clinic Health Essentials. Why is my poop green? 5 causes. With gastroenterologist Christine Lee, MD. Published Jan 8, 2026. health.clevelandclinic.org
Harvard Health Publishing. Green poop: what stool color can indicate about health. Howard E. LeWine, MD. Apr 1, 2024. health.harvard.edu
Northwestern Medicine HealthBeat. Green poop: what's going on? With gastroenterologist Olufemi Kassim, MD. Feb 15, 2025. nm.org
Cleveland Clinic Health Essentials. 15+ foods and supplements that change stool color. With Christine Lee, MD. Published Feb 26, 2025. health.clevelandclinic.org
MedlinePlus Medical Encyclopedia. Stools, pale or clay-colored. Review date Aug 12, 2024. medlineplus.gov
NHS. Side effects of ferrous sulfate. Page last reviewed Feb 9, 2023. nhs.uk
MedlinePlus Medical Encyclopedia. Black or tarry stools. Review date Apr 27, 2026. medlineplus.gov
NHS. Bleeding from the bottom (rectal bleeding). Page last reviewed Apr 12, 2023. nhs.uk
Cleveland Clinic Health Library. Stool (poop) color: guide, what it indicates, healthy color. Last updated Feb 11, 2025. my.clevelandclinic.org
de Vries J, Miller PE, Verbeke K. Effects of cereal fiber on bowel function: a systematic review of intervention trials. World Journal of Gastroenterology. 2015;21(29):8952-63. Funded by a breakfast cereal company. pmc.ncbi.nlm.nih.gov/articles/PMC4528039