Does ZzzQuil Lower Blood Pressure? Understanding the Cardiovascular Effects

October 12, 2025 •

3 min read

In rare instances, taking ZzzQuil can indeed cause a drop in blood pressure, a condition known as hypotension. The over-the-counter sleep aid's active ingredient, diphenhydramine, has documented cardiovascular effects that may impact blood pressure, particularly in certain at-risk populations.

Quick Summary

The active ingredient in ZzzQuil, diphenhydramine, can cause low blood pressure as a rare side effect, especially for older adults or those with pre-existing heart conditions. It can also interact with blood pressure medications, potentially amplifying their effects. Caution and consultation with a doctor are advised, particularly when considering use with other medications.

Key Points

Diphenhydramine is the Active Ingredient: ZzzQuil contains diphenhydramine, a first-generation antihistamine with anticholinergic effects.
Hypotension is a Possible Side Effect: In rare cases, diphenhydramine can cause a decrease in blood pressure, or hypotension, as a side effect.
Increased Risk for the Elderly: Older adults are more susceptible to side effects like dizziness and low blood pressure, which can increase their risk of falling.
Drug Interactions are a Concern: Combining ZzzQuil with prescription blood pressure medications can lead to an additive blood pressure-lowering effect.
Pre-existing Conditions Require Caution: People with cardiovascular diseases or high blood pressure should consult a doctor before taking ZzzQuil.
Read Labels to Avoid Decongestants: Ensure you are not taking a combination product that includes decongestants, which can raise blood pressure.

The Active Ingredient: Diphenhydramine's Effects

ZzzQuil's primary active ingredient is diphenhydramine, a first-generation antihistamine. While its intended purpose is to induce drowsiness by blocking histamine receptors in the brain, it also possesses anticholinergic properties. This dual action can affect various bodily functions, including the cardiovascular system.

How Diphenhydramine Impacts Blood Pressure

Diphenhydramine’s anticholinergic properties can interfere with the body's normal blood pressure regulation. For most healthy adults, this effect is minimal and often unnoticed at standard doses. However, in certain individuals, this mechanism can lead to a decrease in blood pressure, or hypotension.

Potential Mechanisms Leading to Low Blood Pressure:

Anticholinergic Activity: Diphenhydramine blocks muscarinic receptors, which can inhibit the parasympathetic nervous system's tone. This can lead to a decrease in vascular tone, causing vasodilation (widening of blood vessels) and a subsequent drop in blood pressure.
Additive Effects with Other Medications: When taken alongside prescription blood pressure medications, diphenhydramine can compound their hypotensive effects, causing blood pressure to dip too low.
Age-Related Sensitivity: Older adults may be more susceptible to the side effects of diphenhydramine, including sedation, dizziness, and low blood pressure. Their bodies may not regulate blood pressure as effectively, and the drug can increase their risk of falls.

Potential Drug Interactions and Risks

Before taking ZzzQuil, it is crucial to understand its potential to interact with other medications, especially those affecting blood pressure.

Antihypertensives: Individuals taking medications for high blood pressure, such as lisinopril or amlodipine, must be cautious. The combination can lead to an additive blood pressure-lowering effect, increasing the risk of dizziness, lightheadedness, and fainting.
Decongestants: Some cold and sinus relief products that contain diphenhydramine are formulated with decongestants like pseudoephedrine or phenylephrine. Unlike diphenhydramine, these ingredients can increase blood pressure and heart rate by constricting blood vessels. Always read labels carefully to ensure you are taking a single-ingredient product if you have high blood pressure.
CNS Depressants: Combining ZzzQuil with alcohol or other CNS depressants can intensify drowsiness, sedation, and the risk of low blood pressure.

Comparison: ZzzQuil vs. Combination Products

Understanding the specific ingredients in a sleep aid is vital for anyone monitoring their blood pressure. Many different products are available, and their components can have very different effects.


Feature	Single-Ingredient ZzzQuil (Diphenhydramine)	ZzzQuil Cold & Flu (Combination Product)
Active Ingredients	Diphenhydramine	Diphenhydramine, Acetaminophen, and/or Decongestants (e.g., Pseudoephedrine, Phenylephrine)
Primary Effect on BP	Can cause low blood pressure (hypotension) in some individuals, particularly the elderly.	Can raise blood pressure due to decongestants; acetaminophen may also have a mild effect.
Interaction with BP Meds	Can have additive effects with antihypertensives, potentially causing excessively low blood pressure.	Decongestants can counteract the effects of blood pressure medication.
Risk for Hypertensive Patients	Use with caution; consult a doctor due to potential for low blood pressure, especially if taking antihypertensives.	Avoid due to the presence of decongestants, which are known to increase blood pressure.

What to Do If You Have High Blood Pressure

If you have high blood pressure, the best course of action is to speak with your healthcare provider or pharmacist before taking any new over-the-counter medication, including ZzzQuil. They can help you evaluate your specific health profile, including any existing conditions and other medications you are taking, to ensure it is safe for you.

When to Seek Medical Attention

While the risk of severe side effects is low for most, you should seek immediate medical advice if you experience any of the following after taking ZzzQuil:

Dangerously low blood pressure, causing significant lightheadedness or fainting
Very fast heart rate or palpitations
An irregular heartbeat (arrhythmia)
Shortness of breath or chest pain

Conclusion

While a drop in blood pressure is not a typical side effect for all users, ZzzQuil can lower blood pressure due to its active ingredient, diphenhydramine. This risk is amplified for older adults and those already taking blood pressure medication, as the effects can be compounded. The most important takeaway is to understand your own health risks, always read product labels carefully to avoid decongestant-containing versions, and consult a healthcare professional before use, especially if you have pre-existing cardiovascular conditions. Awareness and caution are key to safe use of this and any other over-the-counter medication.

For more detailed pharmacological information on diphenhydramine and its effects, you can consult reputable sources such as Drugs.com.

Frequently Asked Questions

If you have high blood pressure, you should exercise caution and consult with your doctor or pharmacist before taking ZzzQuil. Its active ingredient, diphenhydramine, can cause a drop in blood pressure, and this risk is higher when combined with other blood pressure medications.

Yes, ZzzQuil can interact with blood pressure medications. Its active ingredient, diphenhydramine, may have an additive effect with antihypertensives, potentially causing your blood pressure to drop too low.

The primary ingredient in single-ingredient ZzzQuil is diphenhydramine. It's a first-generation antihistamine that has anticholinergic effects, which can contribute to a decrease in blood pressure.

Products containing only diphenhydramine can potentially lower blood pressure. However, some ZzzQuil products, like cold and flu formulations, also contain decongestants (e.g., pseudoephedrine) that can actually raise blood pressure. Always read the label carefully.

Symptoms of hypotension from ZzzQuil can include dizziness, lightheadedness, and an increased risk of falls, particularly in older adults. In severe cases, it can cause fainting.

Older adults are more susceptible to the effects of diphenhydramine due to age-related changes in drug metabolism and blood pressure regulation. The increased risk of dizziness and sedation also increases their risk of falls.

If you experience symptoms like dizziness, lightheadedness, or palpitations after taking ZzzQuil, you should stop taking it and contact your doctor or pharmacist. If symptoms are severe, seek immediate medical attention.