Last Updated on November 27, 2025 by Bilal Hasdemir

PET Scan Side Effects: Diarrhea and What to Expect

At Liv Hospital, we understand that undergoing a PET scan can make patients feel anxious ” especially when thinking about possible side effects. One common concern is PET scan side effects diarrhea, along with other mild reactions that may occur after the procedure.

A PET scan uses a small, safe amount of radioactive tracer to capture detailed images of how your body’s cells are functioning. While most people experience no major side effects, a few may notice temporary diarrhea, nausea, or fatigue. These effects usually fade within a few hours as the tracer leaves the body.

At Liv Hospital, we make sure every patient feels informed and supported throughout their medical journey. Our team provides clear guidance on what to expect before and after a PET scan, ensuring comfort, safety, and peace of mind.

Key Takeaways

• PET scans are generally safe but may have some side effects.
• Common side effects include reactions at the injection site and gastrointestinal issues.
• Diarrhea is a possible side effect, but it is usually mild and temporary.
• Most side effects resolve within a few hours to 24 hours.
• Liv Hospital provides transparent guidance and support for patients undergoing PET scans.

Understanding PET Scans: What They Are and How They Work

A PET scan, or Positron Emission Tomography scan, is a high-tech medical imaging tool. It gives doctors important insights into the body’s inner workings. This tool is key in spotting and managing health issues like cancer, brain disorders, and heart disease.

To grasp how PET scans function, it’s vital to understand their role in medical diagnostics. They help doctors spot areas where the body’s metabolic activity is off. This can signal disease or dysfunction.

The Purpose of PET Scans in Medical Diagnostics

PET scans are vital for diagnosing and tracking many medical conditions. They shine in oncology, helping spot cancer tumors and check treatment success. Healthdirect.gov.au notes they’re also key in neurology for diseases like Alzheimer’s and Parkinson’s.

The data from a PET scan is key to making treatment choices. It can show if a tumor is reacting to chemo or if a condition is getting worse.

The Role of Radioactive Tracers and Contrast Dyes

PET scans use a radioactive tracer, a tiny amount of radioactive substance injected into the body. This tracer builds up in active areas, like tumors, and emits positrons. The PET scanner catches these positrons to make detailed images.

At times, a contrast dye is added to improve PET scan images. The dye makes certain body parts stand out, aiding in diagnosis.

Knowing about radioactive tracers and contrast dyes is key to understanding PET scans. It shows their importance in medical diagnostics.

Are PET Scan Side Effects Common?

PET scans are a key tool for doctors to diagnose diseases. But it’s important to know about their side effects. These scans use small amounts of radioactive tracers. These are usually safe but can cause problems in some people.

Frequency of Adverse Reactions in Patients

Most people don’t have big problems with PET scans. Studies show that many patients go through them without issues. But it’s key to watch out for any side effects, as some people might be more at risk.

Common side effects include allergic reactions and stomach problems like diarrhea. These issues don’t happen often, but knowing about them helps doctors take care of patients better.

Factors That Increase Risk of Side Effects

Some things can make side effects from PET scans more likely. Allergic reactions are more common in people with allergies. Also, those with kidney disease might face more issues with the contrast dye used in scans.

• History of allergies
• Pre-existing medical conditions (e.g., kidney disease)
• Use of certain medications that may interact with the radioactive tracer or contrast dye

Knowing these risk factors helps doctors prepare and manage any side effects that might happen.

PET Scan Side Effects: Diarrhea: Causes and Duration

PET scans can cause stomach problems like diarrhea. This is something patients should know about. Diarrhea can worry people who are getting tested.

Knowing why and for how long diarrhea happens after a PET scan can help. It can make patients feel better and help them deal with this side effect.

Gastrointestinal Disturbances Following PET Scans

PET scans use radioactive tracers and contrast dyes to see how the body works. These can sometimes upset the stomach, leading to diarrhea in some people.

“The exact mechanism by which PET scans cause gastrointestinal side effects is not fully understood, but it’s believed that the radioactive tracers and contrast agents play a role.”

Expert Opinion

How often and how bad diarrhea is can differ. It depends on the tracer used, the dose, and how sensitive a person is.

Duration of Diarrhea After PET Scans

How long diarrhea lasts after a PET scan varies. But usually, it goes away in a few days.

If diarrhea lasts a long time or is very bad, see a doctor. They can help and offer support.

Understanding why and for how long diarrhea happens after a PET scan helps. It prepares patients for the test and helps them handle stomach problems.

Nausea and Vomiting: Second Most Common Side Effect

PET scan procedures can cause nausea and vomiting in some patients. These are common side effects, more so when contrast material is used.

Causes of Nausea During and After the Procedure

Nausea and vomiting after a PET scan can have different causes. It often comes from the radioactive tracer or contrast dye. Some people might be more sensitive to these substances, causing stomach problems.

Factors contributing to nausea include:

• The type and amount of contrast dye used
• Patient’s overall health and medical history
• Previous experiences with nausea or vomiting

Duration and Management of Digestive Symptoms

The time nausea and vomiting last can differ from person to person. Usually, these symptoms are short-lived and go away in a few hours to a couple of days.

In conclusion, while nausea and vomiting are big side effects of PET scans, knowing why they happen and how to handle them can help. It’s key for patients to follow their doctor’s advice after the scan and seek help if symptoms don’t go away.

Headaches and Dizziness Following PET Procedures

PET scan procedures are usually safe. But some people might feel headaches and dizziness. We’ll look into why this happens and how long it lasts.

Why Some Patients Experience Neurological Symptoms

Headaches and dizziness after a PET scan can happen for a few reasons. It’s often because of how the body reacts to the radioactive tracer. The exact cause can vary from patient to patient, depending on their health and how they process the tracer.

How Long These Symptoms Typically Persist

Mostly, neurological symptoms like headaches and dizziness are temporary. They usually go away within a few hours to a couple of days after the scan. But how long it takes can depend on the person’s health and the tracer used.

Allergic Reactions to PET Scan Tracers and Dyes

PET scans are usually safe, but some people might have allergic reactions to the tracers or dyes. These reactions can be mild or severe. Patients need to know the signs and symptoms.

Common Signs of Mild to Severe Allergic Responses

Allergic reactions to PET scan tracers and dyes can show in different ways. Common signs include:

• Rash or hives
• Itching or swelling
• Redness at the injection site
• Nausea or vomiting
• In severe cases, anaphylaxis, a life-threatening condition requiring immediate medical attention

It’s key for patients to tell their healthcare provider about any allergies before a PET scan. This helps take the right precautions.

Duration of Reactions and When to Seek Medical Attention

The time allergic reactions last can vary. Mild reactions might go away in a few hours to days. But severe reactions, like anaphylaxis, need quick medical help.

Patients should get medical help if they have:

• Difficulty breathing
• Rapid heartbeat
• A significant drop in blood pressure
• Confusion or loss of consciousness

If you’re having these severe symptoms, getting help right away is critical.

Medical experts say, “Knowing the risks and being ready can lessen the worry about PET scans.” Quickly recognizing and treating allergic reactions is vital to avoiding serious problems.

Knowing about allergic reactions and how to react can greatly improve patient safety and results.

Injection Site Reactions: Redness, Pain, and Swelling

PET scans are usually safe, but some people may have reactions at the injection site. These can be redness, pain, or swelling. These reactions happen because of the radioactive tracers used in the scan.

Why Injection Sites May Become Irritated

Several things can irritate the injection site. This includes the type of tracer used, how it’s injected, or how sensitive a person is. It’s important for patients to tell their healthcare provider if they feel any discomfort or unusual reactions.

“The irritation at the injection site is usually mild and goes away quickly,” says A famous medical and radiologist with over a decade of experience. “But it’s key to watch these reactions closely to avoid any serious problems.”

Timeline for Resolution of Localized Symptoms

Mostly, symptoms like redness, pain, and swelling go away in a few days. Using a cold compress or raising the affected arm can help with the pain. If the symptoms don’t get better or get worse, it’s best to see a doctor.

Knowing about injection site reactions and how to handle them can make patients feel more ready for a PET scan. Being well-informed is important for a good experience with any medical test.

Fatigue and Weakness: How Long Recovery Takes

After a PET scan, feeling tired and weak is common. This can make everyday tasks hard. We know that getting a PET scan is a big deal for patients.

Why do people feel so tired after a PET scan? It’s not fully understood. But it’s thought that the radioactive tracers used might affect the body in different ways.

Causes of Post-Procedure Exhaustion

The radioactive tracers in PET scans can make you feel very tired. Also, getting ready for the scan, like fasting, can make you feel weak.

A study found that many patients felt very tired after their PET scan.

“The use of PET scans has become increasingly common in diagnostic medicine, but it’s vital to acknowledge and manage the possible side effects, including fatigue,” said a leading researcher.

Typical Duration Until Energy Levels Normalize

How long you feel tired and weak can vary. But these feelings usually go away in a few days.

Drinking plenty of water and resting well after a PET scan helps your body heal. If you’re feeling tired for a long time, talk to your doctor.

• PET scan-related fatigue is a common side effect.
• Rest and hydration are key for recovery.
• Most people start feeling better in a few days.

PET Scan Radiation Exposure to Family: Safety Facts

When you get a PET scan, you might worry about the radiation it emits. This concern is even more pressing for family members who are pregnant or breastfeeding. We get it; safety is a big deal.

Actual Radiation Levels and Duration in Your System

The radiation from a PET scan is small. It goes down as the radioactive tracer breaks down and leaves your body. The tracer used in PET scans has a short half-life, losing its radioactivity fast.

Radiation Exposure Facts:

Special Precautions for Pregnant Women and Breastfeeding Mothers

If you’re pregnant, tell your doctor before getting a PET scan. The radiation could affect your baby, but the risk is low. Your doctor will take steps to reduce your exposure.

For breastfeeding moms, there’s a worry about the tracer getting into the baby’s milk. We suggest you stop breastfeeding for 24 to 48 hours after the scan, as advised by your healthcare provider.

Knowing the facts about PET scan radiation and following safety tips can help protect your loved ones. Always listen to your healthcare team’s advice to keep everyone safe.

Differences Between PET Scan and CT Scan Contrast Side Effects

PET scans and CT scans are both important in medical imaging. They use different contrast materials, leading to different side effects.

Why CT Contrast More Commonly Causes Diarrhea

CT scans use iodine-based contrast agents, which can upset the stomach and cause diarrhea. On the other hand, PET scans use fluorodeoxyglucose (FDG), a radioactive tracer that is less likely to cause stomach problems. Research shows that CT contrast is more likely to cause diarrhea than PET scan contrast.

The exact reason for CT contrast-induced diarrhea is not fully known. It’s thought that the iodine-based contrast agents might affect how the gut moves and secretes, leading to diarrhea. We will look into this more in our discussion on managing side effects.

Unique Considerations for Combined PET/CT Scans

Combined PET/CT scans are becoming more common. They offer both functional and anatomical information. But using both PET and CT contrast materials together might increase the risk of side effects. Patients should be aware of the possibility of diarrhea, nausea, and allergic reactions.

To reduce these risks, healthcare providers take a detailed approach to patient care. They assess medical history, watch for adverse reactions, and offer personalized advice on managing side effects. We stress the importance of educating and supporting patients to ensure a smooth diagnostic process.

In summary, knowing the differences in side effects between PET scan and CT scan contrast is key for patient care. By understanding the unique side effect profiles of each tool, healthcare providers can better manage patient expectations and offer targeted support.

Conclusion: Preparing for and Managing PET Scan Side Effects

PET scans are a key tool for doctors, but they can cause side effects. It’s important for patients to know about these side effects. This way, they can prepare and manage them better.

PET scan side effects can be uncomfortable. But knowing about them can help lessen their impact. Common side effects include diarrhea, nausea, headaches, and feeling tired. By understanding what to expect, patients can take steps to manage these symptoms and reduce their duration.

To get ready for a PET scan, patients should follow their doctor’s advice. This includes any special diet or drinking lots of water. Managing side effects might mean staying hydrated, resting, and taking medications as told by a healthcare provider. If side effects get worse or don’t go away, patients should see a doctor.

Knowing about PET scan side effects and taking action can make the process easier. If you’re getting a PET scan and worry about side effects, talk to your healthcare provider. They can help with your specific concerns and questions.

FAQ

References

1. National Cancer Institute. (2023). Positron emission tomography (PET) scans. U.S. Department of Health and Human Services, National Institutes of Health. https://www.cancer.gov/about-cancer/diagnosis-staging/screening/pet-scans-fact-sheet