Can Chemo Cause Headaches and What to Do About Them

Chemotherapy can absolutely cause headaches, and for people on certain higher-dose regimens, headaches are among the most common neurological side effects, affecting roughly half to four-fifths of patients in some treatment protocols.¹ The reasons range from direct drug effects on the brain to secondary causes like dehydration, supportive medications, and even the procedures used to deliver chemotherapy. The good news is that most chemo-related headaches are manageable once you and your care team identify what is driving them.

Why Chemotherapy Drugs Trigger Headaches

Despite how common headaches are during chemotherapy, researchers still don’t fully understand all the biological mechanisms behind them. A 2025 review in the International Journal of Molecular Sciences described chemotherapy-related headaches as a “significant challenge” to both well-being and treatment adherence, but acknowledged that the underlying pathways “remain elusive.”² What is known is that different drugs affect the brain and its blood vessels in different ways.

Some agents cause direct irritation to the central nervous system. Methotrexate, especially when given at high doses or injected directly into the spinal fluid, is one of the most well-known offenders. Certain retinoid-based therapies used in specific blood cancers produce headaches in the majority of patients on higher doses, and the headache can become severe enough that doctors have to lower the dose or switch drugs entirely.¹ Cisplatin, 5-fluorouracil, and various targeted therapies have also been linked to headache as a recognized side effect, though the frequency varies widely depending on dose, schedule, and the individual patient.

Beyond direct neurotoxicity, chemotherapy can provoke headaches through indirect routes. Many regimens cause nausea and vomiting, which leads to dehydration and electrolyte imbalances, both classic headache triggers. Chemotherapy can also suppress the immune system, making patients more vulnerable to infections that produce headache as a symptom. And the physical stress of treatment, from poor sleep to anxiety to changes in appetite, creates a background of factors that lower the threshold for headaches in general.

When the Headache Isn’t Really From the Chemo Drug Itself

One of the trickier aspects of headaches during cancer treatment is figuring out which part of the treatment is actually responsible. Chemotherapy rarely happens in isolation. You’re typically also receiving anti-nausea drugs, steroids, pain medications, and sometimes antibiotics or antifungals, each of which can independently cause headaches.

Ondansetron, one of the most widely used anti-nausea medications during chemotherapy, is a good example. A systematic review of ondansetron’s preventive effects on chemotherapy-induced nausea noted that headache is among the drug’s commonly described side effects, along with constipation and mild changes in liver enzyme levels.³ So the very drug intended to make chemotherapy more tolerable can itself trigger head pain. Dexamethasone, another staple of chemo support regimens, can cause headaches both while you’re taking it and during the withdrawal period after stopping.

This layering of medications means that when you develop a headache during a chemo cycle, the cause isn’t always obvious. It could be the chemotherapy agent, the anti-nausea drug, the steroid taper, dehydration from vomiting, or some combination. Your oncology team may need to adjust supportive medications before concluding that the chemotherapy drug itself is the culprit.

Headaches From Lumbar Punctures and Intrathecal Treatment

Some cancers, particularly leukemias and certain lymphomas, require chemotherapy delivered directly into the spinal fluid through a lumbar puncture. This route, called intrathecal administration, ensures the drug reaches the central nervous system, but it introduces its own headache risk that has nothing to do with the drug’s chemistry.

After a lumbar puncture, cerebrospinal fluid can leak from the puncture site, causing a drop in pressure around the brain. The result is a distinctive headache that is worse when sitting or standing upright and improves when lying flat. Pediatric oncology patients are at particular risk for these post-puncture headaches, and they can occur whether the lumbar puncture is for diagnostic testing or for delivering intrathecal chemotherapy.⁴ The headache usually resolves on its own within a few days, but more persistent cases may require a blood patch procedure, in which a small amount of the patient’s own blood is injected near the puncture site to seal the leak.

If you’re receiving intrathecal chemotherapy and develop a headache that gets dramatically worse when you sit up, mention the positional pattern to your team. That detail alone often points to a post-puncture headache rather than a drug side effect, and the management is quite different.

When a Headache During Chemo Is a Warning Sign

Most headaches during chemotherapy are uncomfortable but not dangerous. However, certain patterns demand urgent attention because they can signal serious neurological complications. Two of the most important are posterior reversible encephalopathy syndrome and cerebrovascular events.

Posterior Reversible Encephalopathy Syndrome

Posterior reversible encephalopathy syndrome, known as PRES, is a condition in which the brain develops swelling, typically in the back and sides. It has been linked to a growing number of chemotherapy agents. In one reported case, a 72-year-old man with lymphoma became unresponsive four days after beginning a combination regimen that included rituximab, cyclophosphamide, and intrathecal methotrexate. Brain imaging showed characteristic swelling in the occipital and temporal regions.⁵

In another series, two women with breast cancer developed PRES about a month after their last doses of gemcitabine-based chemotherapy. Both arrived at the emergency department with severe headache, altered mental status, seizures, and high blood pressure. Imaging confirmed swelling in the parieto-occipital regions of the brain.⁶ The word “reversible” in the name is encouraging: with prompt treatment, usually involving blood pressure control and stopping the offending drug, most patients recover. But PRES can cause lasting damage if it goes unrecognized.

The key warning signs that distinguish a PRES headache from an ordinary chemo headache are sudden onset of severe head pain, confusion or difficulty thinking clearly, visual disturbances, seizures, or a spike in blood pressure. Any combination of these warrants emergency evaluation.

Blood Clots in the Brain

Chemotherapy carries a small but real risk of causing blood clots in the arteries or veins of the brain.⁷ This risk is especially relevant during certain treatment phases. For example, in leukemia patients undergoing induction therapy with L-asparaginase, clotting in the large vein that runs along the top of the brain (the superior sagittal sinus) has been documented. Symptoms can include headache alongside seizures and confusion.⁸

Cancer itself increases clotting risk, and chemotherapy adds to that baseline. The practical takeaway is that a new, severe headache that comes with neurological symptoms like weakness on one side, speech difficulty, or a sudden change in vision should be treated as a potential stroke or clot until proven otherwise. Don’t wait to see if it passes.

Metastatic Disease

For anyone actively being treated for cancer, a new or worsening headache always raises the question of whether the cancer has spread to the brain. A review in the journal Cancer emphasized that when patients with cancer describe new headaches, clinicians need to rule out “emergent or concerning etiologies, including metastatic disease,” and outlined red-flag features and imaging approaches for doing so.⁹ Brain metastases tend to produce headaches that worsen over days to weeks, are often worse in the morning, and may come with nausea, balance problems, or personality changes. These patterns differ from the headaches that pop up shortly after a chemo infusion and fade within a day or two, but the distinction isn’t always clean-cut, which is why reporting any new headache pattern to your team matters.

Practical Steps for Managing Chemo-Related Headaches

Once serious causes have been ruled out, you’re left with the everyday reality of head pain during treatment. The approach depends partly on what kind of headache you’re dealing with and partly on what your treatment team considers safe given your current medications and blood counts.

Stay hydrated: This sounds basic, but dehydration is one of the most common and most fixable causes of headache during chemo. Nausea makes it hard to drink, and IV fluids during infusion don’t always make up for the fluid losses from vomiting or reduced intake over the following days. Sipping water, electrolyte drinks, or broth throughout the day, especially in the 48 to 72 hours after a treatment, can make a real difference.
Ask about safe pain relief: Acetaminophen is generally the first-line option during chemotherapy because it doesn’t interfere with platelet function. NSAIDs like ibuprofen are often avoided, particularly when blood counts are low, because they thin the blood and increase bleeding risk. Never take any over-the-counter pain reliever during chemo without checking with your team first. Some drugs interact with specific chemotherapy agents or are risky when your liver or kidneys are already under stress.
Keep a headache diary: Tracking when the headache starts relative to your infusion, how long it lasts, what makes it worse or better, and what other symptoms accompany it gives your team the data they need to figure out the cause. A headache that always peaks on day two after infusion and fades by day four tells a different story than one that shows up unpredictably or keeps getting worse over weeks.
Manage sleep and stress: Chemotherapy disrupts sleep in multiple ways, from steroid-fueled insomnia to anxiety about treatment. Poor sleep is a well-established headache trigger regardless of cancer treatment. Maintaining a consistent sleep schedule, limiting screen time before bed, and addressing anxiety with your care team can reduce headache frequency for some patients.
Cold compresses: Applying a cold pack to the forehead or the back of the neck for 15 to 20 minutes is a simple, low-risk intervention that many patients find helpful, particularly for tension-type headaches.

For patients whose headaches are frequent or severe enough to affect quality of life and treatment adherence, the oncology team may consider adjusting the chemotherapy dose, altering the infusion rate, or switching supportive medications. As research has noted, recognition of how chemotherapy-related headaches affect daily life and treatment adherence is increasingly being integrated into management plans.²

Why Reporting Your Headaches Matters More Than You Think

Patients undergoing chemotherapy tend to underreport side effects, and headaches are no exception. They can feel minor compared to nausea, fatigue, or pain from the cancer itself, so many people simply endure them without mentioning them. This is a missed opportunity. When oncology teams have systematic access to patient-reported symptoms, outcomes improve. A study on symptom monitoring in cancer care found that introducing structured symptom screening led to a measurable improvement in patient satisfaction with care.¹⁰

Beyond satisfaction scores, reporting headaches gives your team clinical information they can act on. A pattern of worsening headaches might prompt imaging to rule out brain metastases. A headache that always follows ondansetron might lead to a switch in anti-nausea medication. A post-infusion headache that responds well to extra hydration might lead your team to add IV fluids to your protocol. None of these adjustments can happen if your doctor doesn’t know about the headache in the first place.

If you find it hard to bring up symptoms during appointments, written logs or patient portal messages work well. Many cancer centers now use electronic symptom-tracking tools that prompt you about specific side effects between visits, which can catch problems earlier than waiting for the next in-person check-in.

Distinguishing Chemo Headaches From Pre-Existing Headache Disorders

A complication that researchers are increasingly focused on is the overlap between chemotherapy-related headaches and headache disorders that already existed before treatment. If you had migraines before your cancer diagnosis, chemotherapy may worsen them, change their pattern, or trigger new episodes. The stress, hormonal shifts, disrupted sleep, and medication changes that come with cancer treatment are all known migraine triggers.

The review in the International Journal of Molecular Sciences specifically highlighted “the need to distinguish chemotherapy-related headaches from primary headache disorders in cancer patients, including migraines or tension-type headaches.”² The distinction matters for treatment. A migraine flare triggered by chemotherapy responds to migraine-specific therapies, while a headache caused by direct neurotoxicity from the drug may require dose adjustment or a different chemotherapy agent. If you have a history of migraines or chronic headaches, make sure your oncology team knows this before treatment starts. It changes the way they interpret and manage any headaches that develop.

Headaches in Children Receiving Chemotherapy

Children undergoing cancer treatment experience many of the same headache-provoking factors as adults, but there are important differences. A review of neurological complications in pediatric cancer patients noted that children, despite often receiving the same types of therapy as adults, may experience different adverse events, and that the child’s ongoing growth and development adds a layer of complexity.¹¹ Younger children may not be able to describe their headache clearly, and behavioral changes like irritability, refusing to eat, or wanting to lie in a dark room may be the only clues.

Children with leukemia are especially likely to undergo repeated lumbar punctures for intrathecal chemotherapy, which means recurrent exposure to the post-puncture headache risk described earlier.⁴ Parents and caregivers should watch for the telltale positional pattern: a child who feels worse when sitting or standing and better when lying down after a lumbar puncture is likely experiencing a fluid-leak headache, and should let the treatment team know.

Headaches From Other Cancer Treatments Used Alongside Chemotherapy

Radiation therapy and immunotherapy, often used in combination with or following chemotherapy, bring their own headache risks. Radiation to the brain, whether whole-brain or focused stereotactic treatment, commonly causes headache from swelling in the treated area. When radiation is combined with immunotherapy drugs, the toxicity profile can overlap. In a phase 1 trial that combined radiation with immunotherapy for brain metastases, headache was one of the grade 3 (severe) toxicities reported.¹²

Immunotherapy drugs on their own can cause headaches through a different mechanism: immune-mediated inflammation. Checkpoint inhibitors, now a standard part of many cancer treatment plans, can trigger inflammation in the brain’s lining or in the pituitary gland (a condition called hypophysitis), both of which produce headache. If you’re receiving a combination of chemotherapy and immunotherapy, pinning down which treatment is causing the headache becomes even more of a detective exercise, and it’s one your oncology team is better positioned to solve if you give them detailed information about the timing and character of the pain.

Hormonal therapies used in breast and prostate cancer can also contribute to headaches through estrogen or testosterone suppression, which is relevant for patients who transition from chemotherapy to long-term hormonal maintenance. The point is that headaches during cancer treatment don’t always end when chemotherapy ends, and understanding the broader landscape of treatment-related head pain helps set realistic expectations.

1
Handbook of Clinical Neurology. Neurological complications of chemotherapy to the central nervous system
2
PubMed Central. Redefining Chemotherapy-Related Headaches: From Pathobiology to Differential Diagnosis and Management
3
PubMed Central. The preventive effects of ondansetron on chemotherapy-induced nausea and vomiting in adult cancer patients: systematic review from ClinicalTrials.gov
4
PubMed. Prevention and management of post-lumbar puncture headache in pediatric oncology patients
5
PubMed Central. Chemotherapy-associated Posterior Reversible Encephalopathy Syndrome: A Case Report and Review of the Literature
6
PubMed Central. Chemotherapy-induced posterior reversible encephalopathy syndrome: Three case reports
7
PubMed. Cerebrovascular complications in patients with cancer
8
Neurologic Clinics. Cerebrovascular Complications in Cancer Patients
9
Wiley Online Library / Cancer. Evaluation of headache in patients with cancer
10
PubMed Central. Additional Value of Patient-Reported Symptom Monitoring in Cancer Care: A Systematic Review of the Literature
11
PubMed Central. Neurological Complications of Pediatric Cancer
12
PubMed Central. Immunotherapy and Radiation Oncology Toxicity of radiation and immunotherapy combinations – Section: Brain