Seeing blood in your dog’s poop after deworming can be concerning, especially if the blood appeared shortly after giving a deworming medication.
You may notice bright red streaks on the outside of the stool, blood mixed into diarrhea, or a change in the stool’s color and consistency.
The timing can be important, but blood in the stool does not automatically mean the dewormer caused an injury or serious complication.
What it means depends on the amount and appearance of the blood, your dog’s bowel movements, appetite, energy level, age, and whether vomiting or other symptoms are present.
Understanding the possible reasons for bloody poop after deworming can help you decide when veterinary assessment is appropriate.
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Dog Poop With Blood After Deworming: Why It Happens
Dog poop with blood after deworming can happen because intestinal irritation, changes in bowel movements, or the underlying parasite infection may affect the digestive tract around the same time the medication is given.
Some dogs can also develop temporary digestive upset after medication.
However, blood in the stool should not automatically be attributed to the dewormer.
The blood may be coming from the underlying intestinal problem, another digestive condition, or a cause that is unrelated to the medication.
Blood in Dog Poop After Deworming: Common Causes
Intestinal irritation from the underlying parasite infection
Intestinal parasites can irritate the lining of the digestive tract.
If the parasite burden is significant, inflammation may already be present before treatment begins.
Passing irritated intestinal contents can result in mucus, loose stool, straining, or small amounts of blood.
In this situation, blood appearing after deworming does not necessarily mean the medication itself caused the bleeding.
Related: Dog pooping bloody mucus but acting normal (Here’s why)
Temporary digestive upset after deworming
Some dogs experience gastrointestinal upset after taking a deworming medication.
Changes in stool consistency, softer stools, diarrhea, nausea, or reduced appetite can occur depending on the medication and the individual dog. Frequent or loose bowel movements can irritate the lower intestinal tract and sometimes result in small streaks of fresh red blood.
Mild digestive changes should still be watched closely, particularly if blood appears or continues.
Intestinal parasites themselves
The parasite being treated may be responsible for some of the intestinal inflammation.
Different parasites affect dogs in different ways. Certain intestinal worms can cause diarrhea, mucus, abdominal discomfort, poor appetite, weight loss, or blood in the stool.
Puppies can be particularly affected by heavy parasite burdens.
If a dog has persistent bloody diarrhea despite deworming, additional testing may be needed rather than simply repeating deworming medication.
Related: Dog loose stool with blood (Causes and treatment)
Straining to poop
Straining or repeatedly passing small amounts of stool can irritate the lower digestive tract.
A dog may develop small amounts of bright red blood on the outside of the stool or near the end of a bowel movement.
This is different from large amounts of blood mixed throughout diarrhea or stool that becomes black and tar-like.
Persistent straining should still be investigated because constipation, colitis, parasites, intestinal irritation, and other conditions can cause it.
Colitis
Colitis is inflammation of the colon and can cause frequent bowel movements, urgency, mucus, straining, and fresh red blood.
A dog may develop colitis around the same time as deworming because of dietary changes, stress, parasites, infections, or other intestinal irritation.
Therefore, the timing of the blood does not necessarily prove that the dewormer caused the colitis.
Dietary upset
A change in food around the time of deworming can also contribute to digestive symptoms.
If your dog received a new food, treats, table scraps, or another dietary change around the same time, diarrhea and intestinal irritation may have more than one possible explanation.
Bacterial or other intestinal infection
Bloody diarrhea can occur with certain intestinal infections.
If the blood is accompanied by frequent diarrhea, vomiting, fever, lethargy, abdominal pain, or loss of appetite, an infection or another significant gastrointestinal problem may need to be considered.
Deworming does not treat every cause of bloody diarrhea.
Medication-related reaction
A dog can occasionally have an adverse reaction to a medication.
Digestive symptoms are among the possible medication-related effects, but the significance depends on the specific drug, dose, the dog’s size and health, and what other medications or substances were given.
If bloody stool began soon after a medication and is accompanied by repeated vomiting, marked weakness, facial swelling, breathing difficulty, or other unusual symptoms, contact a veterinarian promptly.
A separate gastrointestinal problem
Blood in the stool may have nothing to do with deworming.
Foreign material, dietary indiscretion, inflammatory intestinal disease, intestinal obstruction, pancreatitis, gastrointestinal ulcers, and other disorders can cause digestive symptoms and blood in the stool.
If the bloody stool persists or your dog becomes unwell, a veterinarian should determine whether another condition is responsible.
Related: Dog passing blood and not eating (Causes and what to do)
Bright Red Blood in Dog Poop After Deworming
Bright red blood generally indicates relatively fresh bleeding from the lower part of the digestive tract, although the appearance alone cannot determine the exact source.
A few bright-red streaks on otherwise formed stool can occur when the colon or rectum is irritated, particularly after diarrhea or straining.
More concerning patterns include repeated bloody diarrhea, increasing amounts of blood, blood accompanied by significant illness, or stool that becomes very dark or black.
Dog Has Diarrhea and Blood After Deworming
Diarrhea with blood after deworming deserves more attention than a single tiny streak of blood on an otherwise normal bowel movement.
Repeated diarrhea can lead to dehydration, while the underlying cause may be more significant than a simple medication-related stomach upset.
If your dog is repeatedly passing bloody diarrhea, vomiting, refusing food or water, becoming weak, or acting unusually ill, veterinary evaluation is appropriate.
Puppy Pooping Blood After Deworming
Puppies require particular attention when blood appears in their stool.
Puppies commonly receive deworming treatments because intestinal parasites are relatively common in young dogs, but bloody diarrhea can also have other causes.
Young dogs can become dehydrated or seriously ill more quickly than healthy adult dogs.
A puppy with repeated bloody diarrhea, vomiting, marked lethargy, weakness, poor appetite, or other significant changes should be evaluated promptly.
Dog Pooping Blood After Deworming but Acting Normal
If your dog has a small amount of bright red blood in one bowel movement but is otherwise eating, drinking, active, and behaving normally, the situation may be less concerning than persistent bloody diarrhea accompanied by illness.
Even so, normal behavior does not identify the cause.
Keep track of whether the blood appears again, whether the stool becomes increasingly loose, and whether your dog’s appetite, energy, hydration, and bowel habits change.
Continued or worsening blood should be discussed with your veterinarian.
When to Call or Visit the Vet
Contact your veterinarian if your dog has:
Repeated bloody stools or bloody diarrhea
Increasing amounts of blood
Black or tar-like stool
Repeated vomiting
Refusal to eat or drink
Significant lethargy or weakness
Abdominal pain or a swollen abdomen
Frequent straining or inability to pass stool normally
Signs of dehydration
Fever or a marked change in behavior
Persistent diarrhea after deworming
Bloody stool that continues or worsens rather than improving
A heavy parasite burden or previous history of significant intestinal parasites
Seek immediate veterinary attention if there is a large amount of blood, repeated bloody diarrhea with weakness or collapse, severe abdominal pain, repeated vomiting, or a rapidly worsening condition.
Dog Poop With Blood After Deworming: Treatment
Treatment depends on whether the blood is related to intestinal parasites, medication-associated digestive upset, colitis, infection, or another gastrointestinal problem.
The veterinarian may perform a physical examination and recommend fecal testing to look for parasites or other intestinal causes, along with blood tests or abdominal imaging when the symptoms are severe, persistent, or accompanied by other abnormalities.
Treatment may involve addressing the identified parasite or intestinal disease and managing dehydration or other complications.
Key Takeaway
Dog poop with blood after deworming does not necessarily mean the dewormer caused the bleeding.
Intestinal parasites can already irritate the digestive tract, and temporary diarrhea, colitis, straining, dietary upset, or another gastrointestinal condition can also result in blood appearing around the time of treatment.
A small amount of bright red blood in a single bowel movement may be less concerning when a dog otherwise feels well, but persistent or increasing blood should not be ignored.
The appearance of the stool, frequency of bowel movements, and your dog’s overall condition are important clues.
If bloody diarrhea is repeated or accompanied by vomiting, weakness, abdominal pain, poor appetite, dehydration, black stool, or other significant changes, veterinary assessment is important to determine the underlying cause and provide appropriate treatment.