Can Drinking Coffee Cause Changes in Stool Color?

Drinking coffee should not trigger bloody stools or black stools. If you consistently notice blood in your stool after drinking coffee, it’s wise to get checked out by a doctor.

A one-off incident of red stool could be related to your diet. But actual blood in your stool could be caused by conditions of the digestive tract (also called gastrointestinal conditions) that warrant a visit with a gastroenterologist.

Side Effects of Drinking Coffee

Drinking coffee can come with side effects, but black or bloody stool isn’t one of them.

Caffeine can speed up your digestive system, playing a role in diarrhea, according to Harvard Medical School.

Other related side effects of drinking coffee can include heartburn and indigestion, according to the Canadian Digestive Health Foundation. Also, symptoms of any digestive condition that you already have -- like irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and gastroesophageal reflux disease (GERD) -- may get worse.

If you notice blood in your stool after drinking coffee, a condition of the digestive tract may be the cause. Treatment options depend on your exact symptoms, so talk with your doctor about your symptoms.

Many of the effects of coffee on the body are related to the drink’s caffeine content. According to the Mayo Clinic, an 8-ounce (oz) cup of coffee contains around 96 milligrams (mg) of caffeine. Caffeine content varies depending on what coffee beans were used and how strong the coffee was brewed. The U.S. Food and Drug Administration (FDA) recommends that adults limit themselves to around 400 mg of caffeine per day.

Caffeine works by stimulating your central nervous system. You can feel the effects of caffeine as soon as 15 minutes after consuming it, and the substance has a half-life of roughly six hours, according to Cleveland Clinic. It can take up to 10 hours for caffeine to pass through your body entirely.

While many people rely on caffeine daily, consuming too much of it can be harmful. Possible side effects of consuming too much caffeine include:

• Dehydration
• Increased blood pressure
• Headaches
• Feeling dizzy
• Feeling jittery
• Insomnia
• An increased heart rate

Caffeine can be considered an addictive substance, and some people who consume a lot of it may experience caffeine withdrawal when they try to cut down or stop. Symptoms of caffeine withdrawal can include flu-like symptoms, irritability, and trouble concentrating.

Stool Color Changes

Gastrointestinal bleeding can lead to blood in your stool or vomit, according to Mayo Clinic. Common causes of upper-gastrointestinal bleeding include:

• Peptic ulcers
• Inflammation of your esophagus linked to acid reflux
• Tears in your esophagus
• Enlarged veins in the esophagus (called esophageal varices) in people with cirrhosis (advanced liver scarring)

Lower gastrointestinal bleeding can be caused by:

• Hemorrhoids
• Anal fissures
• IBD
• Diverticular disease
• Tumors in your colon

The presence of blood in your stools can contribute to a black or tarry appearance, depending on where the blood is coming from. Black or dark blood in stool typically signifies an upper-gastrointestinal bleed, and bright red blood in stool tends to come from bleeding lower in the gastrointestinal tract, according to Cleveland Clinic.

If you pass stool with the appearance of ground coffee, blood in your stool is a potential culprit. If you notice you’re passing black stool, seek care from a gastroenterologist urgently.

The presence of blood may make your stool appear red, but another potential culprit is your diet. Food and drinks that contain red food coloring can make your bowel movements red, and so can eating lots of red-colored fruits and vegetables like beetroot and cranberries, according to Cleveland Clinic. Similarly, orange foods like carrots can contribute to orange-red stools.

‘Coffee Grounds’ in Vomit

If you have vomit that looks like coffee grounds, it’s likely a sign of coagulated blood in your vomit, according to Mayo Clinic. Get medical care for this right away. Vomiting blood can be a symptom of potentially serious conditions, including:

• Liver failure
• Cirrhosis
• Various types of cancer, including cancer of the stomach, pancreas, or esophagus
• Peptic ulcers
• Tearing or inflammation in the gastrointestinal tract

Watch for any symptoms of shock or severe blood loss related to vomiting blood that require immediate medical attention, including:

• Fainting
• Nausea
• Confusion
• Blurred vision
• Dizziness
• Shallow breathing
• Low urine output
• Clammy, cold skin