Colorectal cancer is one of the deadliest forms of cancer because most people do not experience any symptoms in the early stages. Reports show that more than 60% of cases do not receive a diagnosis until after the cancer has spread. Being aware of all of the potential symptoms of colorectal cancer are the best ways to catch any complications early.

The symptoms of colorectal cancer are not unique and could indicate any number of other, less serious issues. However, if any of these symptoms persist for more than a few days, it is best to see a doctor.


One of the main symptoms of colorectal cancer—and the first people tend to notice—is a change in bowel habits. This often takes the form of a change in stool consistency, such as diarrhea.

Sometimes, dizziness accompanies diarrhea, usually when the person stands up from sitting on the toilet.

person entering the bathroom



Another potential form of a change in bowel habits is constipation. Like diarrhea, the duration and severity varies significantly, though doctors can prescribe some medications if it becomes a notable issue.

Drinking plenty of fluids and eating high-fiber foods helps improve bowel movement frequency and consistency. Without any treatment, constipation from colorectal cancer can lead to fecal impaction or bowel obstruction.


Alternating Diarrhea and Constipation

While both constipation and diarrhea can indicate colorectal cancer, they are also common symptoms of irritable bowel syndrome and many other issues. The more telling sign of cancer is if a person frequently alternates between constipation and diarrhea and if they also experience unintended weight loss, extreme fatigue, and blood in the stool.

When these symptoms occur together, they suggest cancerVisiting a medical professional immediately is key.


Rectum Feels Full

In the early stages of colorectal cancer, a person may feel like they need to use the bathroom at unusual times. Performing a bowel movement does nothing to alleviate this sensation.

This sensation may also feel similar to gas or bloating, or simply feeling full. For some, the sensation presents as cramps or sharp pain in the abdomen.

woman with stomach pain because of bowel issues


“Pencil” Stools

As tumors grow, the intestinal passage slowly narrows. Over the progression of the cancer, the development of scar tissue and strictures can further shrink the passage.

This leads to stools that are extremely narrow in shape. These stools can be as narrow as a pencil, earning them the nickname “pencil” stools.

digital illustration of tumor in intestine


Pain With Defecation

Also called dyschezia, intense pain while attempting to defecate is a common symptom of colorectal cancer. In adults, dyschezia typically occurs alongside constipation.

Like constipation, dyschezia often causes straining during bowel movements, which may worsen the pain. Additionally, bowel movements may increase in length and take longer than 10 minutes to complete.

woman in pain on the toilet


Blood in the Stool

As colorectal cancer worsens, blood may be visible in the stool. If the tumor is near the rectum, the blood may be bright red. If a tumor is further up in the colon, the blood will have a dark red or maroon color.

Many different issues can cause blood in the stool, so visiting a doctor is the best way to determine the problem.

doctor speaking seriously with patient and their son



Around 48% of people with colorectal cancer develop symptoms of iron deficiency anemia, which also has links to worse short-term prospects, including longer hospital stays and a higher risk of mortality.

Iron deficient anemia is also difficult to manage in individuals with colorectal cancer, as iron therapy may stimulate tumor growth.

gloved hand holding an anemia test vial of blood



Due to the physical strain that colorectal cancer causes, as well as symptoms like bleeding and anemia, people with the condition often feel fatigued, which usually combines extreme tiredness with weakness or general weariness that is not relieved by sleeping.

Fatigue is often a result of low red blood cell counts and one of the earliest symptoms to manifest.

older woman looking exhausted or fatigued sitting on bed


Unwanted Weight Loss

Undesired weight loss is almost always a sign of a condition that requires medical attention. As colorectal cancer enters the advanced stages, systemic inflammation can trigger both muscle and weight loss.

It also leads to a notable lack of appetite, which exacerbates weight loss.

woman standing on bathroom scale checking weight


Black, Tarry Stools

In the later stages of colorectal cancer, bleeding often occurs in the upper gastrointestinal area. Digestive enzymes and intestinal bacteria cause hemoglobin in the blood to slowly darken in the long passage toward the rectum. As a result, stools take on a dark color with a sticky, tar-like texture. The medical term for this is melena.

barium xray of colon and intestines



Narrowing of the gastrointestinal passage due to tumor growth and strictures can continue to limit bowel movements if an individual does not receive treatment. Over time, this leads to bowel obstructions.

If the blockage is large enough, visible ballooning of the rectum. Without treatment, these blockages are potentially deadly, which is why it is so vital to visit a medical professional when experiencing severe constipation or alternating diarrhea and constipation.

xray of the colon and intestines


Nausea and Vomiting

Throughout the course of colorectal cancer progression, each symptom can contribute to a general sense of being unwell. Typically, the body deals with this through nausea and vomiting.

During the early stages, these symptoms often appear alongside persistent abdominal discomfort. As obstruction becomes more severe, both nausea and vomiting may increase in severity and frequency.

young man looking sick with nausea


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