How Does ZzzQuil Work for Insomnia?

ZzzQuil, an over-the-counter sleep aid that contains the generic drug diphenhydramine, is used to treat people experiencing difficulty falling or staying asleep.

This article discusses how ZzzQuil works to treat insomnia and some of the potential common and serious side effects of using it. It also covers how it works and whether it may help you sleep better.

Uses for ZzzQuil

ZzzQuil is sold over the counter, meaning that you don't need a prescription to purchase it. Sold as a liquid or a liquid-filled capsule, ZzzQuil is a sleep aid that is used to treat insomnia characterized by difficulty falling or staying asleep.

ZzzQuil's active ingredient, diphenhydramine, is most often used to provide relief from allergies; sleepiness is a side effect of this component. However, since diphenhydramine is the medication's only active ingredient, it is advertised as safer than other "PM" sleeping pills that may also contain Tylenol (acetaminophen), ibuprofen, or other ingredients. It should be taken when you can devote eight hours to sleep to avoid morning side effects.

How ZzzQuil Works

Diphenhydramine belongs to the group of medications called antihistamines. Antihistamines block the action of the chemical histamine, a signal within the central nervous system that promotes wakefulness. As a result, antihistamine medications can lead to drowsiness.

Diphenhydramine is only modestly effective in improving sleep, according to research. Studies suggest that people fall asleep on average about eight minutes faster compared to placebo. The total amount of sleep improves by an average of about 12 minutes.

Who Can Use It

Speak with your healthcare provider if you're concerned about how ZzzQuil may affect your health or interact with your other medications. In general, it should not be used in children under 12, and it should be used with caution in older people.

Some of the conditions that may require additional caution when considering the use of ZzzQuil include:

• Glaucoma
• Hyperthyroidism
• Heart disease
• High blood pressure
• Asthma
• Chronic obstructive pulmonary disease (COPD)
• Pneumonia
• Peptic ulcer disease
• Prostate enlargement
• Obstruction of the bowel or bladder

If you have any of these conditions, you should speak with your healthcare provider before starting to use ZzzQuil. As this medication has the potential to interact with other drugs, especially those that impact the brain, review your medications with your healthcare provider or pharmacist before using it.

Insomnia Healthcare Provider Discussion Guide

Get our printable guide for your next healthcare provider's appointment to help you ask the right questions.

Download PDF

Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life.

Email Address

Sign Up

You're in!

Thank you, {{form.email}}, for signing up.

There was an error. Please try again.

Dosage for ZzzQuil

The recommended dosage is one 30 milliliter (mL) dose per 24 hours for adults and children 12 years and older.

Side Effects of ZzzQuil

Diphenhydramine and histamine work within the brain as well as other parts of the body, causing the potential for side effects. Diphenhydramine can also suppress a cough or nausea and may lead to uncontrolled movements called dyskinesias.

Morning "hangover" effects may occur with the use of the medication, especially if:

• Inadequate time is spent in bed after taking it.
• Higher doses are taken.
• It is taken with other medications.
• You have certain medical conditions, including untreated sleep disorders like sleep apnea.

Side effects when taking ZzzQuil may include:

• Confusion (delirium)
• Clumsiness
• Drowsiness
• Dizziness
• Increased pressure within the eye
• Headache
• Stomach upset
• Dry mouth or nose
• Hyperactivity
• Constipation
• Thick lung secretions
• Difficulty urinating
• Low blood pressure
• Blurry or double-vision
• Rapid or irregular heart rate
• Light sensitivity
• Sweating
• Erectile dysfunction

Potential Serious Reactions

As with the use of any drug, there are also risks of serious side effects with the use of ZzzQuil. These are more rare but may include:

• Anaphylaxis (severe allergic reaction including difficulty breathing)
• Low blood cell counts (including anemia)
• Abnormal heart rhythms
• Seizures
• Toxic psychosis (characterized by confusion and abnormal behaviors)
• Acute labyrinthitis (inner ear problems)

Precautions

As noted above, certain people are advised to use ZzzQuil with caution, or not at all. As it is an over-the-counter medication, there may be an impression that the overall risks are lower compared to other prescription medications used to treat insomnia. This may not be the case, however, so review the best sleep remedies for you with your healthcare provider.

For pregnant women, harm to a developing fetus is possible but unlikely. In addition, ZzzQuil is probably safe during lactation, though caution is advised.

Given the limited effectiveness of this medication, it may be desirable to pursue other treatment options for insomnia.

Summary

ZzzQuil is an over-the-counter sleep aid that contains diphenhydramine as the active ingredient. It is used to treat insomnia, but studies show it is not a very effective sleep aid. ZzzQuil can have side effects, including dizziness, confusion, drowsiness, low blood pressure, and more. People with certain health conditions should use caution when taking ZzzQuil.

If your daily activities are affected by poor sleep or sleep problems persist for several weeks, talk with your healthcare provider about the best sleep aid options for you and whether further evaluation by a sleep specialist is warranted.