Does Benadryl Thin Your Blood?

Does Benadryl Thin Your Blood

Benadryl, also known as diphenhydramine, is a normally used antihistamine medication. It is primarily used to treat symptoms of allergies such as sneezing, runny nose, itching, and watery eyes.

However, some people have questioned whether Benadryl can also act as a blood thinner. The short answer is yes, it does have some properties that can thin your blood.

Let’s take a closer look at how this medication affects your body and what you need to know about its potential effects on your blood.

Understanding Benadryl

To understand how Benadryl affects your blood, it is important to first understand how this medication works.

How Does Benadryl Work?

Benadryl functions by blocking the action of histamine, a substance in the body that triggers allergic symptoms.

When you have an allergic reaction, your body releases histamine, which attaches to receptors in your body, causing symptoms like swelling, itching, and increased mucus production.

By blocking these receptors, Benadryl helps to alleviate these symptoms.

Common Uses of Benadryl

Besides treating allergy symptoms, Benadryl is used for:

  • Motion sickness
  • Insomnia
  • Common cold symptoms
  • Dermatologic conditions like hives and itching

It’s crucial to understand that Benadryl does not cure these conditions but offers temporary relief.

What is Blood Thinning?

Blood thinning is a term used to describe the process of reducing the blood’s ability to clot.

Clotting is an essential process that aids your body to heal wounds and stop bleeding. However, when there is too much clotting in your blood, it can lead to serious health issues like stroke or heart attack.

Blood thinners work by preventing blood clots from forming or dissolving existing clots.

Types of Blood Thinning Medications

There are two main types of blood thinning medications:

  1. Anticoagulants – such as warfarin and heparin, slow down the body’s clotting process.
  2. Antiplatelet drugs – like aspirin and clopidogrel, inhibit platelets from clumping together to form a blood clot.

Can Benadryl Cause Blood Thinning? The Truth

Can Benadryl Cause Blood Thinning?

As mentioned earlier the short answer is that Benadryl can thin your blood.

The possible reasons for this are:

  1. Anticholinergic Effects: Benadryl has anticholinergic properties, meaning it blocks the action of acetylcholine, a neurotransmitter involved in blood clotting. This can slow your body’s clot formation.
  2. Interactions with Other Medications: Benadryl may interact with other medications, such as blood thinners or NSAIDs (non-steroidal anti-inflammatory drugs), enhancing their effects. This can excessively thin the blood.
  3. Large Doses: Taking large doses of Benadryl can also heighten the risk of bleeding due to its anticoagulant properties, especially in older adults who are more sensitive to the medication’s effects.

Also Read: Can Ozempic Cause Blood Clots?

Research and Studies

Several studies have been conducted to investigate the potential blood thinning effects of Benadryl.

One study published in the American Journal of Emergency Medicine found that diphenhydramine can cause a significant increase in bleeding time, indicating its potential to thin blood.

Another research article published in Chest examined the effects of antihistamines on blood clotting in patients with asthma. It concluded that antihistamines can increase bleeding time, potentially increasing the risk of bleeding.

Factors Influencing Blood Thickness

It’s essential to note that the effects of Benadryl on blood thickness may vary from person to person.

This is because several factors can influence how your body responds to the medication, including:

  • Age: As you age, your body’s ability to process and eliminate medications decreases, making you more susceptible to their effects.
  • Health Conditions: Pre-existing health conditions, especially those related to the liver or kidneys, can affect how Benadryl is metabolized, potentially altering its effects on blood thickness.
  • Concurrent Medication Use: Taking Benadryl alongside other medications that affect blood clotting can amplify its blood-thinning properties.
  • Dosage and Duration: The amount of Benadryl taken and the duration of use can influence its impact on your blood. Higher doses and prolonged use may increase the risk of thinning blood.

Potential Side Effects of Benadryl

While Benadryl has several potential uses, it also comes with some side effects.

If you are taking this medication or considering using it, here are some possible side effects to watch out for:

Increased Risk of Bleeding: As discussed above, Benadryl can potentially thin your blood and increase the risk of bleeding.

Increased Drowsiness: Benadryl can cause drowsiness as a common side effect. This may be enhanced when taken with other medications or alcohol.

Dry Mouth and Eyes: Dryness of the mouth and eyes is another common side effect of Benadryl, which may increase the risk of gum disease and dental problems.

Difficulty Urinating: Benadryl can also cause difficulty urinating, especially in men with an enlarged prostate.

Increased Heart Rate: In some cases, Benadryl may increase your heart rate, which may be concerning for individuals with heart conditions.

Precautions to Take

To minimize the risk of blood thinning and other potential side effects, here are some precautions to consider when taking Benadryl:

  1. Consult with your doctor: If you have any pre-existing health conditions or take other medications, it is essential to consult with your doctor before using Benadryl.
  2. Follow dosage instructions: Stick to the advised dosage and duration of use to avoid potential complications.
  3. Monitor your symptoms: If you experience any concerning side effects, such as increased bleeding or difficulty urinating, seek medical attention immediately.
  4. Avoid alcohol consumption: Alcohol can intensify the drowsiness caused by Benadryl, making it unsafe to drive or operate machinery while taking this medication.

Alternative Allergy Medications

If you are concerned about the potential blood-thinning effects of Benadryl, there are other allergy medications that do not have similar properties. Some examples include:

Loratadine – This is a non-drowsy antihistamine medication that does not cause blood thinning.

Flonase – A nasal spray containing corticosteroids that can reduce inflammation and symptoms of allergies without affecting blood thickness.

Montelukast – A medication commonly used for asthma and allergies that does not thin the blood.

Debunking Myths

There are several misconceptions about Benadryl and its effects on blood thickness. Here are some of the most common myths debunked:

Benadryl can prevent a heart attack.

While it is true that diphenhydramine can dilate blood vessels, this does not necessarily mean it can prevent a heart attack.

It’s safe to mix Benadryl and alcohol.

Both Benadryl and alcohol can cause drowsiness, so combining the two can enhance this effect, potentially leading to accidents or injuries.

Taking more than the recommended dose of Benadryl will increase its effectiveness.

Taking too much Benadryl can actually have harmful effects and may not be more effective in treating allergies.


In conclusion, Benadryl has anticoagulant properties that can thin the blood and increase the risk of bleeding. However, this effect may vary depending on factors such as age, health conditions, and dosage.

Key Takeaways

  • Benadryl can potentially thin the blood and increase the risk of bleeding.
  • Several factors may influence how your body responds to Benadryl, including age, health conditions, concurrent medication use, dosage, and duration of use.
  • It’s essential to consider potential side effects and take precautions when using Benadryl to minimize any risks.
  • There are alternative allergy medications available that do not have blood-thinning properties.
  • It’s important to debunk myths about Benadryl and its effects on blood thickness for accurate information.


Can too much Benadryl cause bleeding?

Yes, taking too much Benadryl can thin the blood and increase the risk of bleeding. It’s essential to follow recommended dosage instructions.

Can I take Benadryl if I am on blood thinners?

It is not recommended to take Benadryl if you are on blood thinners, as it can amplify their effects and increase the risk of bleeding.

Is it safe to give my child Benadryl for allergies?

It is best to consult with a doctor before giving Benadryl to children, especially if they have any pre-existing health conditions. It’s also crucial to adhere to the correct dosage guidelines based on their age and weight.

Can I take Benadryl before surgery?

It is not recommended to take Benadryl before surgery, as it can potentially increase the risk of bleeding during and after the procedure.

Is Benadryl harmful to the heart?

Taking Benadryl in recommended doses is generally safe for individuals with a healthy heart. However, those with pre-existing heart conditions should consult with their doctor before using this medication.

Useful Resources

WebMD- Benadryl

Healthline- What Does It Mean to Have Thin Blood?

MedicalNewsToday- Benadryl (diphenhydramine)


The content of this article is provided for informational purposes only and should not be considered a replacement for professional medical advice, diagnosis, or treatment. It is important to seek professional medical advice and not disregard it or delay seeking it based on the information read here. While we strive to provide accurate and reliable information, we cannot guarantee its completeness, accuracy, reliability, suitability, or availability for any purpose. Using the information in this document is your responsibility and carries inherent risks. We are not liable for any losses or damages resulting from the use of our content.


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