Stomach bleeding can show up as visible changes in your vomit or stool, or it can be completely hidden, revealing itself only through symptoms like unusual fatigue or dizziness. The signs depend on how fast the bleeding is and where it’s coming from. Upper gastrointestinal bleeding affects 50 to 150 people per 100,000 each year and carries a mortality rate of 5 to 15%, so recognizing the warning signs early matters.
Visible Signs in Your Stool
The most telling sign of stomach bleeding is a change in your stool’s color and texture. Because blood from the stomach has to travel through the entire digestive tract before it comes out, it gets broken down along the way. By the time it reaches your stool, it no longer looks red. Instead, your stool turns black, sticky, and tarry, with a distinctly foul smell. This type of stool is called melena, and it points specifically to bleeding in the stomach or upper digestive tract.
Black stool from stomach bleeding looks and feels different from dark stool caused by iron supplements or certain foods like blueberries. The tarry, almost shiny consistency and the unusually strong odor are what set it apart. If your stool is bright red or maroon, that typically signals bleeding lower in the digestive tract, such as the colon or rectum, not the stomach.
What Vomiting Blood Looks Like
Vomiting blood is another clear signal, but it doesn’t always look the way you’d expect. If the bleeding is active and heavy, you may vomit bright red blood. More often, though, the blood has been sitting in your stomach long enough to be partially digested by stomach acid. This gives it a grainy, dark appearance that resembles coffee grounds. The color can range from dark red to brown to black, depending on how long the blood has been there.
Coffee-ground vomit means the bleeding isn’t necessarily happening right at that moment. The blood had time to coagulate and darken before your body expelled it. Either way, vomiting anything that looks like blood or coffee grounds warrants immediate medical attention.
Hidden Bleeding You Can’t See
Not all stomach bleeding is obvious. Slow, low-volume bleeding can go unnoticed for weeks or months because the amount of blood lost each day is too small to visibly change your stool. This is called occult bleeding, and it commonly shows up as iron-deficiency anemia rather than anything you can see in the toilet.
The symptoms of this slow blood loss build gradually. You might notice increasing fatigue, weakness, shortness of breath during activities that used to feel easy, pale skin, or feeling lightheaded when you stand up. These are all signs your body is running low on red blood cells because it can’t replace them as fast as you’re losing them. Many people chalk these symptoms up to stress or poor sleep before discovering the real cause.
A stool test can detect this hidden blood. The most common version is a fecal immunochemical test (FIT), which checks for traces of blood invisible to the naked eye. These tests are highly specific, correctly ruling out blood more than 96% of the time, but their sensitivity for catching problems varies. They’re a useful first step, not a definitive answer.
Signs of Severe or Rapid Bleeding
When stomach bleeding is heavy, the symptoms escalate quickly. Losing 15 to 30% of your blood volume raises your heart rate above 100 beats per minute and speeds up your breathing, even though your blood pressure may still appear close to normal. You might feel anxious, thirsty, or slightly confused.
Once blood loss exceeds about 30%, your blood pressure drops noticeably, your heart races above 120 beats per minute, and your mental state changes. You may feel confused, disoriented, or faint. At 40% or more, the situation becomes life-threatening, with dangerously low blood pressure and altered consciousness. These signs can develop over hours or, in severe cases, minutes. Feeling dizzy or fainting alongside any of the stool or vomit changes described above is a medical emergency.
What Causes Stomach Bleeding
Peptic ulcers are the leading cause. These are open sores in the stomach lining or the first part of the small intestine, most commonly caused by a bacterial infection (H. pylori) or long-term use of anti-inflammatory painkillers like ibuprofen, aspirin, or naproxen. Many people with ulcers experience a dull or burning stomach pain, often worse between meals or at night, along with bloating, nausea, or heartburn. But some people have no pain at all until the ulcer starts bleeding.
NSAID use deserves special attention because the risk is dose-dependent. Even low-dose aspirin at 75 mg per day more than doubles the risk of a bleeding ulcer. At 300 mg per day, the risk nearly quadruples. Higher doses of other NSAIDs follow the same pattern: medium daily doses roughly double the risk, while high daily doses increase it nearly fivefold. This doesn’t mean everyone who takes ibuprofen will bleed, but regular use over weeks or months significantly raises the odds, especially in older adults or people taking blood thinners at the same time.
How Stomach Bleeding Is Diagnosed
If your symptoms suggest active bleeding, the primary diagnostic tool is an upper endoscopy. A thin, flexible camera is passed through your mouth into your stomach, allowing a doctor to see exactly where the bleeding is coming from and, in many cases, treat it during the same procedure. For acute bleeding, guidelines recommend this be done within 24 hours. If the bleeding is severe or the patient is unstable, it’s typically performed within 12 hours.
For suspected slow or hidden bleeding, the process usually starts with blood tests to check for anemia and a stool sample to look for occult blood. If those come back positive, endoscopy follows to locate the source.
What to Watch For
Stomach bleeding doesn’t always announce itself dramatically. The combination of signs worth paying attention to includes black or tarry stools, vomit that looks like coffee grounds, unexplained fatigue or weakness that worsens over time, and lightheadedness or dizziness. If you’re taking NSAIDs regularly and develop new stomach pain, that’s also a warning sign worth acting on. Roughly 90% of significant gastrointestinal bleeding originates from the upper digestive tract, making the stomach and the area just beyond it the most common sources.