What drugs can lower white blood cell count? A pharmacological overview

October 13, 2025 •

3 min read

According to the National Institutes of Health, drug-induced leukopenia is a known and well-documented adverse drug effect. This condition, characterized by an abnormally low white blood cell count, can be caused by a wide array of prescription and over-the-counter medications and can lead to an increased risk of infection.

Quick Summary

Many medication classes, including chemotherapy, immunosuppressants, and antipsychotics, are known to decrease white blood cell counts. This can heighten a person's vulnerability to infections and requires careful medical monitoring and management to mitigate risks.

Key Points

Chemotherapy and Myelosuppression: Chemotherapy drugs commonly and predictably cause a low white blood cell count (leukopenia) by suppressing bone marrow function.
Clozapine's Risk: The antipsychotic clozapine has a known, though rare, risk of causing a dangerously low white blood cell count called agranulocytosis, requiring mandated regular blood testing.
Immunosuppressants Impact: Medications used to suppress the immune system, such as azathioprine and methotrexate, can dose-dependently lower white blood cell counts.
Antibiotics and Idiosyncratic Reactions: Certain antibiotics, like penicillins and cephalosporins, can cause leukopenia through an unpredictable, immune-mediated reaction, especially with high doses or prolonged use.
Monitoring is Crucial: Regular blood work is essential for patients on high-risk medications to detect and manage a dropping white blood cell count before complications like infection occur.
Early Detection is Key: Vigilance for signs of infection (e.g., fever) is critical for patients experiencing drug-induced neutropenia, regardless of the cause.

Introduction to Drug-Induced Leukopenia

Leukopenia is a medical condition in which the number of white blood cells (WBCs) circulating in the blood is lower than normal. As WBCs are a critical component of the immune system, a low count can leave the body more susceptible to infection. When medication is the cause, it is known as drug-induced leukopenia. This adverse effect can be a dose-dependent consequence of myelosuppression (bone marrow suppression), or it can be a rare, unpredictable, idiosyncratic reaction. The risk of developing drug-induced leukopenia varies depending on the specific medication, dosage, and individual patient factors.

Primary Medication Classes that Lower WBC Count

Many different types of medications can lead to a reduced white blood cell count through various mechanisms, including direct bone marrow suppression or immune-mediated reactions. Some of the primary classes are discussed below.

Chemotherapy Agents

Chemotherapy drugs are a leading cause of leukopenia, particularly neutropenia (low neutrophil count). These medications target rapidly dividing cells, impacting both cancer cells and healthy cells in the bone marrow responsible for producing white blood cells. This myelosuppression results in decreased WBC production, and the severity depends on the specific drug and dosage.

Common examples: Cyclophosphamide, paclitaxel, gemcitabine, and methotrexate are frequently associated with reduced WBC counts.
Management: Regular blood monitoring is standard during chemotherapy. Hematopoietic growth factors like G-CSF may be used to stimulate neutrophil production.

Immunosuppressants

Immunosuppressive medications, used for transplant patients and autoimmune diseases, can lower WBC counts as they suppress the immune system. This is often a dose-dependent side effect.

Common examples: Azathioprine, mycophenolate mofetil, tacrolimus, methotrexate, and rituximab are often linked to leukopenia.
Mechanism: These drugs can be toxic to the bone marrow or interfere with WBC production.

Antipsychotic Medications

Certain antipsychotics can cause leukopenia or agranulocytosis (a severe drop in granulocytes). While rare, it can be serious. The cause can be immune-mediated or due to bone marrow toxicity.

Most notably: Clozapine has a significant association with agranulocytosis and requires mandatory blood monitoring.
Other examples: Olanzapine, risperidone, and paliperidone have also been linked to this side effect in less frequent cases.

Antibiotics

Some antibiotics can cause leukopenia, typically through an unpredictable immune reaction. The risk can increase with higher doses or longer treatment.

Examples: Beta-lactam antibiotics like penicillins and cephalosporins are common examples. Trimethoprim-sulfamethoxazole, minocycline, and vancomycin have also been associated with neutropenia.

Anti-inflammatory Drugs

Certain anti-inflammatory medications can decrease WBC counts.

Examples: Some NSAIDs like ibuprofen have rarely been reported to cause neutropenia. Anti-rheumatic drugs like sulfasalazine and methotrexate are also known causes in some individuals.

Anticonvulsants

Some anticonvulsant or anti-seizure medications may cause temporary leukopenia.

Examples: Carbamazepine is a known cause, often in the initial months of treatment. Valproate, oxcarbazepine, and phenytoin have also been linked to this side effect.

Comparing Drug Classes Associated with Leukopenia


Drug Class	Primary Mechanism	Common Examples	Severity/Frequency	Monitoring Requirements
Chemotherapy	Direct bone marrow suppression	Cyclophosphamide, Gemcitabine	High, often dose-dependent	Routine blood counts (weekly/bi-weekly)
Immunosuppressants	Immune system suppression, bone marrow toxicity	Azathioprine, Mycophenolate Mofetil	Variable, often dose-dependent	Regular blood monitoring
Antipsychotics	Idiosyncratic immune reaction, bone marrow toxicity	Clozapine (high risk), Olanzapine	Low incidence, but potentially severe (agranulocytosis)	Mandatory frequent monitoring for clozapine
Antibiotics	Immune-mediated destruction, idiosyncratic	Penicillins, Cephalosporins, Minocycline	Low incidence, can be dose/duration-dependent	Monitoring for prolonged courses or high doses
Anticonvulsants	Direct marrow toxicity, idiosyncratic	Carbamazepine, Valproate	Low incidence, often transient	Initial and periodic blood count checks
Anti-inflammatories	Immune-mediated, idiosyncratic	Sulfasalazine, Methotrexate, NSAIDs	Low incidence, dose-dependent with some agents	Varies; monitoring recommended for long-term use

Conclusion

Numerous medications can lower white blood cell counts, with varying risks depending on the drug class. Chemotherapy and some immunosuppressants are high-risk categories requiring close monitoring due to their predictable, dose-related effects on the bone marrow. Other drugs, such as certain antipsychotics, antibiotics, and anti-inflammatories, carry a lower but still significant risk, often through unpredictable reactions. Patients should be vigilant for signs of infection and report them to their doctor promptly. Careful monitoring and patient education are crucial for managing these medications safely.

For detailed information on specific medication side effects, consult your prescribing physician or a pharmacist. The Mayo Clinic also provides information on conditions like neutropenia.

Frequently Asked Questions

Drug-induced leukopenia is a condition where a person's white blood cell count drops below the normal range as a side effect of taking a medication. This can be a result of bone marrow suppression or an immune-mediated reaction to the drug.

Chemotherapy drugs are a primary cause of leukopenia, as they attack rapidly dividing cells, including those in the bone marrow. Examples include cyclophosphamide, gemcitabine, and methotrexate, with the risk often dependent on dosage and regimen.

The antipsychotic medication clozapine is well-known for its potential to cause agranulocytosis, a severe form of neutropenia. This risk is primarily due to an idiosyncratic reaction and requires mandatory, regular blood monitoring during treatment.

Yes, some antibiotics can cause a mild to moderate decrease in white blood cell count, particularly beta-lactam antibiotics like penicillins and cephalosporins, especially with high doses or prolonged use. This typically occurs through an immune reaction.

A low white blood cell count itself often has no symptoms. However, it increases the risk of infection, so symptoms may include fever, mouth sores, swollen lymph nodes, or a rash. In severe cases, it can lead to serious infections.

Management typically involves discontinuing or adjusting the dose of the offending drug. Depending on the severity and cause, a doctor may also prescribe granulocyte-colony stimulating factor (G-CSF) to help boost white blood cell production.

No, but some anticonvulsants, such as carbamazepine, phenytoin, and valproate, have been linked to leukopenia. This effect is often transient and typically occurs at the beginning of therapy, but monitoring is advised.