The role of Benadryl in cancer treatment
Diphenhydramine, commonly known by the brand name Benadryl, is a first-generation antihistamine used to relieve symptoms of allergies like sneezing, runny nose, and itching. During cancer treatment, its use goes beyond common allergies, often serving specific roles prescribed by an oncology team. The first and most common use is as a premedication to prevent hypersensitivity reactions to certain chemotherapy drugs. These reactions can range from mild to severe, and administering an antihistamine beforehand can significantly reduce the risk. Your provider may administer Benadryl intravenously (IV) in a clinical setting or prescribe an oral dose to take before your appointment.
Beyond its role as a premedication, Benadryl can also be used to manage other challenging side effects of cancer treatment. Its sedative properties can be leveraged to address anxiety and insomnia, though this should only be done under a doctor's recommendation due to the risk of excessive drowsiness. It may also be prescribed to help alleviate chemotherapy-induced nausea and vomiting (CINV) when used in combination with other anti-nausea medications. Additionally, Benadryl's anti-itch properties can be useful for patients experiencing itching or rashes, which can be a side effect of some treatments.
Benadryl and immunotherapy
Recent research has uncovered a potentially beneficial interaction between certain antihistamines and cancer immunotherapy, a treatment distinct from chemotherapy. Some studies suggest that H1-antihistamines (the class Benadryl belongs to) may improve responses to immune checkpoint inhibitors by counteracting the immunosuppressive effects of histamine released by tumors. This does not mean patients should start self-medicating with Benadryl. The studies are still ongoing, and any such use would be part of a highly controlled, medically supervised treatment plan. For patients on standard chemotherapy, this effect does not apply.
Important safety considerations
The importance of doctor approval
Never take Benadryl or any other over-the-counter (OTC) medication without first checking with your oncology care team. What might seem like a simple allergy medicine could have serious consequences in the context of cancer treatment. Your doctor needs to have a full and accurate list of all medications you are taking, including herbal supplements and vitamins. Not all chemo drugs are compatible with Benadryl, and some cancer types or co-existing health conditions may contraindicate its use.
Drug interactions
Benadryl can interact with several medications, which is a major reason for medical supervision during chemo.
- CNS Depressants: Combining Benadryl with other CNS depressants, such as certain pain medications, anti-anxiety drugs, or sedatives, can amplify side effects like drowsiness and sedation. This could be particularly dangerous if a patient also receives these medications as part of their cancer regimen.
- Tamoxifen: For breast cancer patients, there is a known interaction where Benadryl may reduce the effectiveness of the hormone therapy drug tamoxifen. This is a crucial consideration that only a doctor can properly assess.
- Other OTCs: Be aware that many common cold and flu remedies also contain diphenhydramine. Combining these with a separate Benadryl dose can lead to an overdose.
Potential side effects
Common side effects of Benadryl include drowsiness, dizziness, and confusion. These can be more pronounced in cancer patients, especially those who are already weakened or taking other medications. Benadryl's anticholinergic effects can also cause dry mouth, constipation, and blurred vision. In rare cases or high doses, more serious cardiovascular effects, including palpitations or an abnormal heart rhythm, can occur.
First-generation vs. second-generation antihistamines
Choosing the right antihistamine can be an important discussion with your oncologist. Benadryl is a first-generation antihistamine, known for causing significant drowsiness because it crosses the blood-brain barrier. Newer, or second-generation, antihistamines are generally non-drowsy. Your care team may have a preference depending on your specific needs.
| Feature | First-Generation Antihistamines (e.g., Benadryl) | Second-Generation Antihistamines (e.g., Claritin) |
|---|---|---|
| Effectiveness | Effective for allergy symptoms, can also treat insomnia and nausea. | Also effective for allergy symptoms, but generally not used for sedation or CINV. |
| Sedation | High. Causes significant drowsiness, dizziness, and impaired coordination. | Low to none. Designed to be non-drowsy. |
| Side Effects | Dry mouth, blurred vision, constipation, dizziness, confusion. | Fewer side effects, typically limited to mild drowsiness in some individuals. |
| Interaction Risks | Higher risk of interaction with other CNS depressants and specific drugs like tamoxifen. | Lower risk of CNS interactions, though professional consultation is always necessary. |
| Use in Chemo | Commonly used as a premedication or for specific side effect management under medical supervision. | Sometimes recommended for bone pain associated with certain injections (e.g., loratadine for Neulasta) or general allergies. |
Conclusion
Yes, it is possible to take Benadryl while on chemotherapy, but this must be done under the strict guidance and approval of your oncology care team. Whether used as a premedication to prevent allergic reactions or to manage specific side effects like nausea or itching, its purpose and safety must be carefully evaluated against your individual treatment plan. Potential drug interactions and significant side effects, particularly drowsiness, make self-medication a dangerous practice during cancer treatment. Always inform your healthcare provider of any over-the-counter products you are considering, as they can recommend the safest and most effective options for your situation.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. For specific medical guidance, consult with your oncology team.
For more information on medication safety during cancer treatment:
Dana-Farber Cancer Institute: Safety Information for Patients
