Chemotherapy can cause low blood pressure through several different mechanisms, ranging from immediate allergic-type reactions during an infusion to slower nerve damage that impairs the body’s ability to regulate blood pressure over weeks or months. The most common route is an infusion-related reaction, but drugs like vincristine, doxorubicin, and newer immunotherapy agents each have their own distinct ways of driving blood pressure down. Understanding which mechanism is at work matters because the treatment for each one is different.
Infusion Reactions Are the Most Common Cause
The single most frequent reason blood pressure drops during chemotherapy is an infusion-related reaction, essentially the body’s immune system overreacting to the drug as it enters the bloodstream. This can look a lot like a severe allergic reaction: blood pressure plummets, the skin may flush or break out in hives, and the patient can develop chills, chest tightness, or difficulty breathing. Most chemotherapy-associated drops in blood pressure stem from this allergic-type mechanism.1PubMed Central. Irinotecan-induced severe hypotension in a patient with lung cancer
These reactions can happen with a wide range of drugs, but some are more notorious than others. Rituximab, a drug used for lymphoma and certain autoimmune conditions, has been documented to cause severe blood pressure drops within minutes of starting an infusion. In one reported case, a patient’s blood pressure fell to 76/45 within five minutes of the first dose, with no prior exposure to the drug. When clinicians tried again at a slower rate, the blood pressure dropped a second time.2PubMed. Rapid development of infusion-related severe hypotension during rituximab therapy That speed and severity is the hallmark of an infusion reaction: it happens fast, it is directly tied to the drug entering the vein, and it usually resolves once the infusion is stopped and supportive treatment is given.
Infusion rate matters. Giving a drug too quickly increases the chance that the body mounts this kind of reaction, which is why oncology nurses typically start certain drugs at a low drip rate and gradually increase it. Premedication with steroids and antihistamines is standard practice for drugs known to carry a high reaction risk. Even so, reactions can still break through, which is why blood pressure monitoring during infusion sessions is routine.
Nerve Damage That Disrupts Blood Pressure Regulation
Your body keeps blood pressure stable through an automatic system you never have to think about. When you stand up, nerves signal your blood vessels to tighten and your heart to beat a little faster, keeping blood flowing to your brain. Certain chemo drugs, particularly the vinca alkaloids like vincristine, can damage those nerves. The result is called autonomic neuropathy, and its most noticeable symptom is orthostatic hypotension, a sudden drop in blood pressure when you go from sitting or lying down to standing.
Vincristine is well known for causing peripheral neuropathy (tingling and numbness in the hands and feet), but it also damages the autonomic nerves that control cardiovascular reflexes. Research suggests roughly a third of patients treated with vincristine develop some degree of autonomic dysfunction, with measurable decreases in heart-rate and blood-pressure responses during activities like standing or gripping.3PubMed Central. Cardiovascular Autonomic Dysfunction Before and After Chemotherapy in Cancer Patients Unlike an infusion reaction, which happens during or right after a dose, autonomic neuropathy builds up over time. A patient might feel fine during the first few cycles but begin having dizzy spells weeks or months into treatment.
The mechanism involves damage to the nerves that control norepinephrine release, one of the main signals that tells blood vessels to constrict. In one early case, a patient on vincristine for about a year developed severe orthostatic hypotension and was found to have virtually no norepinephrine output. After vincristine was stopped, norepinephrine levels returned to normal within about six weeks, though blood pressure recovery was slower and incomplete.4JAMA Internal Medicine. Orthostatic Hypotension During Vincristine Therapy The autonomic damage from vincristine tends to improve after treatment ends, but recovery can take anywhere from months to years.3PubMed Central. Cardiovascular Autonomic Dysfunction Before and After Chemotherapy in Cancer Patients
This kind of blood pressure problem is particularly tricky because it is posture-dependent. A patient’s blood pressure might read perfectly normal while lying in a hospital bed but drop sharply the moment they stand. If the care team only checks blood pressure in one position, they can miss it entirely.
When Chemo Weakens the Heart Itself
Some chemotherapy drugs are directly toxic to heart muscle cells. Doxorubicin, one of the most widely used and effective chemo drugs, is the best-known example. It works by interfering with cancer cell DNA, but heart cells are collateral damage. The injury is cumulative: higher total doses cause progressively more harm. In animal studies, higher cumulative doses of doxorubicin produced significant drops in systolic, diastolic, and mean blood pressure along with marked reductions in heart rate, while lower doses did not cause measurable changes.5PubMed Central. Doxorubicin Dose-Dependent Impact on Physiological Balance—A Holistic Approach in a Rat Model
In humans, this manifests as cardiotoxicity that can range from a subtle decline in the heart’s pumping efficiency to overt heart failure. A weakened heart simply cannot push blood through the body hard enough to maintain normal pressure. Unlike an infusion reaction, which is dramatic and immediate, cardiotoxicity from doxorubicin can appear months or even years after the last dose. Oncologists track this by monitoring the heart’s ejection fraction (how much blood the heart pumps out with each beat) before, during, and after treatment. When they set lifetime dose limits for doxorubicin, they are trying to stay below the threshold at which the cumulative damage becomes clinically dangerous.
Capillary Leak and Vascular Leak Syndromes
A less well-known but potentially life-threatening cause of low blood pressure during cancer treatment involves the blood vessels themselves becoming leaky. In capillary leak syndrome, the tiny blood vessels that exchange fluid between the bloodstream and surrounding tissues lose their ability to hold fluid inside. Plasma leaks out into tissues and body cavities, blood volume drops, and blood pressure falls, sometimes catastrophically. Severe cases can progress to cardiovascular collapse and organ failure.6PubMed Central. Systemic Capillary Leak Syndrome (SCLS) Presentation in Patients Receiving Anti-cancer Treatments
High-dose interleukin-2 (IL-2), used as immunotherapy for cancers like melanoma and kidney cancer, is the classic trigger. IL-2 is potent against tumors, but at the doses needed to be effective, it provokes a storm of immune signaling that damages the lining of blood vessels. The exact pathway is still being worked out, but it appears to involve a cascade of immune activation including complement system activity, neutrophil engagement, and changes in the molecules that hold vessel walls together.7European Respiratory Journal. Interleukin-2 – induced vascular leak syndrome: clinically relevant in vitro recapitulation with a patient-derived lung-on-chip The severity is dose-dependent: higher IL-2 doses produce worse leakage, which is one of the major factors limiting how aggressively clinicians can use this drug.8PubMed Central. An immune competent in vitro model of IL2 induced vascular leakage enables mechanistic insights and evaluation of mitigation strategies
This mechanism is different from a simple allergic reaction. In capillary leak syndrome, fluid pours out of the bloodstream into the tissues, causing visible swelling alongside the low blood pressure. A patient may gain several pounds of fluid weight in a short time while simultaneously becoming hypotensive, a counterintuitive combination that tips clinicians off to what is happening.
Immunotherapy and Adrenal Insufficiency
Newer immunotherapy drugs, particularly checkpoint inhibitors like nivolumab and pembrolizumab, have introduced a blood-pressure-lowering mechanism that oncology teams are still getting used to. These drugs work by releasing the brakes on the immune system so it can attack cancer cells more effectively. But an unleashed immune system can also attack the body’s own organs, including the pituitary gland and adrenal glands. When those glands are damaged, the body loses its ability to produce cortisol, a hormone essential for maintaining blood pressure.
The resulting condition, adrenal insufficiency, causes blood pressure to drop and stay stubbornly low even with intravenous fluids. In one case, a patient on nivolumab for lung cancer came to the emergency department in shock with a blood pressure of 68/48 and a heart rate of 141. His cortisol level, which had been normal two months earlier, had plummeted. He recovered rapidly after receiving intravenous hydrocortisone.9PubMed Central. Refractory hypotension due to Nivolumab-induced adrenal insufficiency Similar cases have been reported with pembrolizumab, where patients develop persistent low blood pressure, fatigue, and low sodium levels weeks to months after starting treatment.10PubMed Central. Immunotherapy Induced Adrenal Insufficiency: An Underdiagnosed Cause of Persistent Hypotension in Cancer
Adrenal insufficiency from immunotherapy is considered rare, reported in roughly one percent of patients on these drugs.11PubMed Central. Nivolumab Induced Adrenal Insufficiency: Rare Side-effect of a New Anti-cancer Therapy – Immune-checkpoint Inhibitors But it is almost certainly underdiagnosed. The symptoms, fatigue, weakness, nausea, and low blood pressure, overlap heavily with general side effects of cancer treatment, making it easy for clinicians to attribute them to the disease or the chemo itself rather than ordering the hormone tests that would reveal the real problem. A morning cortisol level is the key screening test: if it comes back abnormally low in someone on a checkpoint inhibitor, adrenal insufficiency should be high on the list. The combination of ipilimumab and nivolumab appears to carry a higher risk, as one case report documented secondary adrenal insufficiency in a patient who had been on the combination for about two months before symptoms emerged.12Endocrine Practice. When Cancer Therapy Strikes the Pituitary: Secondary Adrenal Insufficiency From Immunotherapy
Infections and Sepsis During Treatment
Chemotherapy suppresses the bone marrow, which makes infection-fighting white blood cells. When the white cell count drops low enough, a state called neutropenia, the body becomes vulnerable to infections that a healthy immune system would easily contain. If bacteria enter the bloodstream during this window, the resulting condition, neutropenic sepsis, can cause blood pressure to drop dangerously fast. Sepsis-related low blood pressure is not caused by the chemo drug directly, but it would not have happened without the immune suppression that chemotherapy created.
Neutropenic sepsis is a medical emergency. The combination of fever and a critically low white cell count requires immediate antibiotics and often intensive-care-level support. Blood pressure drops in sepsis because the body’s inflammatory response causes widespread blood vessel dilation and fluid leakage, a mechanism somewhat similar to capillary leak syndrome but driven by infection rather than the drug itself. Oncology teams try to prevent this scenario with prophylactic antibiotics and growth factor injections that stimulate white blood cell production, but it remains one of the most dangerous complications of cytotoxic chemotherapy.
Vascular Damage and Long-Term Effects
Some chemotherapy drugs damage the inner lining of blood vessels (the endothelium) in ways that create problems extending well beyond the treatment period. Cisplatin, a platinum-based drug used widely for testicular, ovarian, and lung cancers, is a prime example. Research on patients with testicular cancer found that cisplatin-based chemotherapy induces direct toxic effects on the endothelium, increasing stress signaling in vessel walls and reducing the body’s natural ability to break down blood clots.13JACC: CardioOncology. Comprehensive Characterization of the Vascular Effects of Cisplatin-Based Chemotherapy in Patients With Testicular Cancer
This endothelial damage is more associated with cardiovascular events like blood clots and, paradoxically, sometimes high blood pressure due to increased arterial stiffness. But in the acute setting, the vascular injury contributes to the general cardiovascular instability that cancer patients on multi-drug regimens experience. The broader point here is that chemotherapy affects the entire cardiovascular system in complex ways. Blood pressure can go in either direction depending on which drugs are used, how the vessels respond, and how the heart adapts.
Practical Steps for Managing Low Blood Pressure During Treatment
If you are going through chemotherapy and dealing with low blood pressure, the first and most important step is making sure the cause has been correctly identified. As the sections above illustrate, the treatment for an infusion reaction (stop the drug, give epinephrine and antihistamines) is completely different from the treatment for adrenal insufficiency (hormone replacement) or autonomic neuropathy (physical countermeasures and medication adjustments). Ask your oncology team whether a specific cause has been investigated, especially if the low blood pressure is persistent rather than occurring only during infusions.
For orthostatic hypotension specifically, whether caused by autonomic neuropathy or by the general deconditioning and dehydration that come with cancer treatment, there are several evidence-based strategies. A review of orthostatic hypotension management identifies a core set of non-drug approaches: reviewing all current medications for blood-pressure-lowering effects (many cancer patients are on additional drugs that lower blood pressure as a side effect), increasing salt and fluid intake, wearing compression garments, and making behavioral changes like rising slowly from a seated position.14PubMed. Management of Orthostatic Hypotension: A Review
One case report illustrates how multifactorial chemotherapy-related low blood pressure can get. A patient with orthostatic hypotension complicated by chemo-induced autonomic neuropathy did not improve with intravenous fluids alone. The care team had to stop other medications that were worsening the problem, bring in physical therapy, use an abdominal binder to push blood back toward the core, and minimize the time the patient spent lying flat (which paradoxically makes orthostatic drops worse when you finally stand).15Providence Digital Commons. A Case Of Multifactorial Orthostatic Hypotension Complicated By Chemotherapy Associated Autonomic Toxicity The lesson is that low blood pressure during chemo is rarely a single-cause problem, and fixing it often means addressing several contributing factors at once.
The Growing Role of Cardiovascular Monitoring in Cancer Care
The field of cardio-oncology has expanded significantly over the past decade, driven in part by the recognition that cancer treatments affect the heart and blood vessels in ways that were historically underappreciated. Modern cardio-oncology programs aim to catch cardiovascular problems early, before they become clinical emergencies, using a combination of risk assessment tools, imaging, and blood tests for cardiac biomarkers.16PubMed Central. Cardiovascular Risk Stratification and Surveillance in Cardio-Oncology: Mechanistic Foundations and Future Directions This is a shift from the older approach, where cardiovascular side effects were dealt with only after they became obvious.
For patients on drugs like doxorubicin, this typically means echocardiograms at regular intervals to track heart function. For those on checkpoint inhibitors, it may mean periodic hormone panels to screen for adrenal or thyroid problems. If you are starting a chemotherapy regimen that carries known cardiovascular risks, ask whether a baseline cardiovascular assessment is appropriate. Many cancer centers now have dedicated cardio-oncology consultants who work alongside the oncology team to manage these overlapping risks. The goal is not to avoid effective cancer treatment but to use it as safely as possible while catching complications early enough to intervene.