Understanding What Lowers Your White Blood Cell Count: A Look at Medications and Medical Conditions

October 13, 2025 •

3 min read

According to the American Cancer Society, a low white blood cell count is a common side effect of strong chemotherapy, putting patients at increased risk of infection. Knowing what lowers your white blood cell count is critical, as numerous medications and underlying medical conditions can lead to this concerning health issue. A low WBC count, or leukopenia, can weaken the immune system and requires careful monitoring.

Quick Summary

A low white blood cell (WBC) count, known as leukopenia, can result from various factors, including side effects of medication, particularly chemotherapy, radiation therapy, and some antibiotics. It may also stem from medical conditions like autoimmune disorders, infections, and bone marrow problems.

Key Points

Chemotherapy and radiation therapy often cause leukopenia by damaging bone marrow stem cells, which produce white blood cells.
Immunosuppressant drugs, like azathioprine and rituximab, are designed to inhibit the immune system and can significantly lower WBC counts.
Certain antibiotics, particularly beta-lactams and sulfa drugs, can induce neutropenia, a specific type of leukopenia.
Autoimmune diseases, such as lupus and rheumatoid arthritis, can cause the body's immune system to attack its own WBCs.
Infections, including viruses like HIV and hepatitis, or severe bacterial infections like sepsis, can also lead to a low WBC count.
Nutritional deficiencies of vitamin B12, folate, and copper can impair the bone marrow's ability to produce blood cells.
Medication-induced leukopenia usually resolves after discontinuing the offending drug, but should only be done under a doctor's supervision.
Symptoms of leukopenia are often related to the infections that result from a weakened immune system, such as fever, chills, and mouth sores.

The Role of White Blood Cells and Leukopenia

White blood cells (WBCs), or leukocytes, are a crucial part of the immune system, helping to defend the body against infection and disease. A low white blood cell count, or leukopenia, occurs when the number of these infection-fighting cells drops below the normal range, leaving the body more vulnerable to infections. Most white blood cells are produced in the bone marrow, so conditions or treatments that affect bone marrow health are often the primary cause of leukopenia. Understanding these causes is the first step toward effective management and prevention of severe complications.

How Medications Lower Your WBC Count

Many medications can inadvertently suppress white blood cell production as a side effect.

Chemotherapy and Radiation Therapy: Bone Marrow Suppression

Cancer treatments like chemotherapy and radiation are among the most common causes of low WBC counts. These therapies damage the bone marrow cells that produce white blood cells. The lowest point of the WBC count after chemotherapy is known as the nadir, typically occurring 7 to 10 days after treatment.

Immunosuppressants: Preventing White Blood Cell Production

Medications that suppress the immune system, used for autoimmune diseases or to prevent organ transplant rejection, can decrease white blood cells. Examples include azathioprine, mycophenolate mofetil (CellCept), and rituximab.

Antibiotics: Drug-Induced Neutropenia

Certain antibiotics can cause drug-induced neutropenia, a decrease in neutrophils, a type of WBC. Beta-lactam antibiotics (like penicillin and cephalosporins) and sulfonamides are examples. Vancomycin has also been linked to neutropenia.

Other Medications Affecting WBC Count

A variety of other drugs can lower WBC counts, including certain antipsychotics (like clozapine), anticonvulsants, antithyroid drugs, some NSAIDs, and certain antidepressants.

Medical Conditions That Cause a Low WBC Count

Beyond medication, several medical conditions can lead to leukopenia.

Autoimmune Disorders: Targeting Healthy Cells

In autoimmune conditions, the immune system attacks healthy cells, including WBCs. Examples include lupus and rheumatoid arthritis.

Infections: Viral and Bacterial Causes

Both viral (like HIV, hepatitis, Epstein-Barr) and severe bacterial infections (like sepsis) can cause a drop in WBCs. Other infections such as tuberculosis and malaria are also known causes.

Bone Marrow Problems: Production Issues

Problems affecting the bone marrow's ability to produce blood cells can cause leukopenia. These include aplastic anemia and certain cancers like leukemia and lymphoma.

Nutritional Deficiencies

Deficiencies in nutrients like vitamin B12, folate, or copper can impair blood cell production.

Medication-Induced Leukopenia vs. Other Causes

It is important to differentiate between the causes of leukopenia. The table below compares key features of medication-induced leukopenia with other common causes.


Feature	Medication-Induced Leukopenia	Other Medical Conditions
Cause	Triggered by a drug.	Infection, autoimmune attack, or bone marrow dysfunction.
Onset	Often occurs after a specific duration of treatment.	Can be acute or chronic.
Resolution	Typically resolves after the drug is discontinued.	Varies based on the underlying condition.
Management	Stopping the drug is often primary.	Treatment targets the underlying disease.
Severity	Can range from mild to severe.	Can also vary, potentially life-threatening.

Symptoms and Risks of a Low WBC Count

Leukopenia itself often does not cause symptoms; instead, the symptoms arise from the increased risk of infection. A low WBC count can lead to frequent infections and serious complications. Signs of infection include fever, chills, sore throat, severe cough, painful urination, and skin infection.

Conclusion: Consulting a Healthcare Professional

A low white blood cell count requires a thorough investigation to determine the cause, whether medication-related or due to an underlying condition. Consult a healthcare provider for diagnosis and to review your medical history and medications. Do not stop prescribed medication without consulting your doctor, who can determine the best course of action.

For more in-depth information on managing conditions related to low WBCs, you may find additional resources from authoritative sources, such as the Centers for Disease Control and Prevention on protecting against infection during chemotherapy.

Frequently Asked Questions

Chemotherapy drugs are the most well-known cause of a low white blood cell (WBC) count, but other common medications include immunosuppressants, certain antibiotics (especially beta-lactams and sulfonamides), antipsychotics like clozapine, and some anticonvulsants.

Yes, some antibiotics can cause a decrease in WBCs through a reaction known as drug-induced neutropenia. Penicillins, cephalosporins, and sulfonamides are examples of antibiotics that have been associated with this side effect.

Autoimmune disorders, such as lupus and rheumatoid arthritis, can cause the body's immune system to attack and destroy its own white blood cells, leading to a chronically low count.

A low WBC count, or leukopenia, weakens your immune system and increases your risk of developing infections. If the count is very low, even minor infections can become serious or life-threatening.

The recovery time for a WBC count depends on the medication and individual. In cases of drug-induced neutropenia, the count usually begins to normalize after the causative drug is discontinued, but it can take several days to weeks.

Yes, deficiencies in certain vitamins, particularly vitamin B12 and folate, can impair the production of white blood cells in the bone marrow, leading to a low count.

A low WBC count itself doesn't have direct symptoms, but the first sign is often a fever or other symptoms of an infection, such as mouth sores, chills, or a persistent cough, due to a weakened immune system.