How many hours does ZzzQuil (diphenhydramine) last?

ZzzQuil (diphenhydramine) usually lasts about [4 to 6 hours](https://www.goodrx.com/benadryl/benadryl-bad-for-sleep) after you take it. But you might still feel sleepy the next morning, especially if you don’t get a full night of sleep.

How long does ZzzQuil (diphenhydramine) take to kick in?

ZzzQuil (diphenhydramine) generally kicks in within [30 minutes](https://www.goodrx.com/benadryl/benadryl-bad-for-sleep). Since it works quickly, it’s best to take it close to your usual bedtime rather than too early.

Is ZzzQuil (diphenhydramine) bad for your kidneys?

Although rare, diphenhydramine, the active ingredient in ZzzQuil and Benadryl, has been [linked to kidney damage](https://www.goodrx.com/benadryl/is-it-bad-for-your-liver-or-kidneys). This is very uncommon and usually gets better after stopping the medication and getting treatment. If you have [kidney problems](https://www.goodrx.com/conditions/kidney-disease) or take other [medications that affect your kidneys](https://www.goodrx.com/health-topic/kidneys/damaging-medications), talk to your primary care provider or kidney specialist before using ZzzQuil (diphenhydramine).

What's the difference between ZzzQuil and NyQuil?

ZzzQuil and [NyQuil](https://www.goodrx.com/nyquil/what-is) are made by the same company, which is why their names sound similar, but they’re used for different reasons. ZzzQuil products are made to help with sleep and often contain ingredients like [melatonin](https://www.goodrx.com/melatonin/what-is) or antihistamines that cause drowsiness. NyQuil products are made to treat cold and flu symptoms and usually contain a mix of ingredients for congestion, cough, pain, fever, and runny nose. Check with your pharmacist or primary care provider if you have questions [comparing](https://www.goodrx.com/compare/zzzquil-vs-nyquil) the two.

ZzzQuil (diphenhydramine): Uses, Side Effects, Dosage & More

What is ZzzQuil (diphenhydramine)?

What is ZzzQuil (diphenhydramine) used for?

Occasional trouble sleeping - people 12 years and older

How ZzzQuil (diphenhydramine) works

ZzzQuil (diphenhydramine) is an antihistamine. It blocks histamine, a chemical in your brain that helps keep you awake. By blocking histamine, ZzzQuil (diphenhydramine) makes you feel sleepy and can help you fall asleep faster.

Are you looking for information on diphenhydramine (Benadryl) instead?

Drug facts

Common Brands	ZzzQuil
Drug Class	Antihistamine
Controlled Substance Classification	Not a controlled medication
Generic Status	Lower-cost generic available
Availability	Over-the-counter

Common Brands

ZzzQuil

Drug Class

Antihistamine

Controlled Substance Classification

Not a controlled medication

Generic Status

Lower-cost generic available

Availability

Over-the-counter

More on ZzzQuil (diphenhydramine) essentials

A woman holding a glass of water prepares to take a pill before bed time.
Prostock-Studio/iStock via Getty Images Plus

Benadryl for Sleep: What to Know About This Antihistamine’s Sleepy Side Effects

Written by Jennifer Gershman, PharmD, CPh, PACS

Side effects of ZzzQuil (diphenhydramine)

The following side effects may get better over time as your body gets used to the medication. Let your healthcare provider know immediately if you continue to experience these symptoms or if they worsen over time.

Common Side Effects

Sleepiness during the day
Dizziness
Constipation
Blurry vision
Dry mouth

Less Common Side Effects

Headache
Stomach upset
Trouble urinating
Weakness
Hyperactivity (more common in children)

ZzzQuil (diphenhydramine) serious side effects

Contact your healthcare provider immediately if you experience any of the following.

Excessive sleepiness or dizziness

Source: DailyMed

The following ZzzQuil (diphenhydramine) side effects have also been reported

Side effects that you should report to your care team as soon as possible:

Allergic reactions—skin rash, itching, hives, swelling of the face, lips, tongue, or throat
Sudden eye pain or change in vision such as blurry vision, seeing halos around lights, vision loss
Trouble passing urine

Side effects that usually do not require medical attention (report these to your care team if they continue or are bothersome):

Pros and cons of ZzzQuil (diphenhydramine)

Pros

Available over the counter
Comes as pills and liquid that you take by mouth
Starts to work within 30 minutes

Cons

Not typically recommended because it hasn’t been shown to help much
Can make you feel sleepy during the day
Can worsen certain conditions like glaucoma and stomach ulcers

Pharmacist tips for ZzzQuil (diphenhydramine)

Use ZzzQuil (diphenhydramine) for sleep only for short periods. If sleep problems continue, talk to your primary care provider.
ZzzQuil (diphenhydramine) can make you sleepy and dizzy the next day. Don’t drive or do anything that needs focus until you know how it affects you.
Avoid alcohol while taking ZzzQuil (diphenhydramine). Alcohol can make sleepiness and dizziness worse.
ZzzQuil (diphenhydramine) can cause dry mouth. To help with dry mouth, consider chewing on sugar-free gum, sucking on ice, rinsing with cold water, or using saliva sprays or lozenges.
ZzzQuil (diphenhydramine) might not be safe for older adults. It can raise the risk of falls because it can make you feel dizzy, tired, or cause a drop in your blood pressure. Talk to your primary care provider to be safe.
If you're taking ZzzQuil (diphenhydramine) liquid, measure doses with the device that comes with it or ask your pharmacist for one. Don't use household spoons because they can give the wrong dose.
Don't take ZzzQuil (diphenhydramine) with other antihistamines since it can raise your risk of side effects. Many cold or allergy products already contain antihistamines, so check labels carefully.
Don’t use ZzzQuil (diphenhydramine) to make a child sleep. It can sometimes make children more active instead of sleepy, so talk to a pediatrician for safer options.

Common questions about Zzzquil

Zzzquil usually lasts about 4 to 6 hours after you take it. But you might still feel sleepy the next morning, especially if you don’t get a full night of sleep.

Zzzquil generally kicks in within 30 minutes. Since it works quickly, it’s best to take it close to your usual bedtime rather than too early.

It’s best to avoid taking Zzzquil every night. If needed, you can use it nightly for up to 2 weeks, but don’t use it longer unless a healthcare professional tells you to. Ongoing sleep problems that last more than 2 weeks could point to a more serious condition, so it’s important to get checked by a healthcare professional.

No, you should only take one 50 mg dose of Zzzquil in a 24-hour period. Taking more than one dose can raise your risk of side effects, such as next-day sleepiness, dizziness, and problems with balance or coordination. If 50 mg doesn’t help you sleep, talk to your primary care provider about other treatment options.

Zzzquil isn't considered addictive. But taking it too often can make you rely on it to fall asleep. Rare cases of misuse have been reported, especially with high dose or long-term use. Talk to your primary care provider if you have questions about whether this medication is safe for you.

Although rare, diphenhydramine, the active ingredient in ZzzQuil and Benadryl, has been linked to kidney damage. This is very uncommon and usually gets better after stopping the medication and getting treatment. If you have kidney problems or take other medications that affect your kidneys, talk to your primary care provider or kidney specialist before using Zzzquil.

Technically yes. Both ZzzQuil and Benadryl are basically the same medication. They both contain the same active ingredient, diphenhydramine, and work the same way in your body. The main difference is how they’re marketed: ZzzQuil is labeled for sleep, while Benadryl is labeled for short-term relief of allergy or cold symptoms. Contact your pharmacist or primary care provider if you have questions comparing the two.

ZzzQuil and NyQuil are made by the same company, which is why their names sound similar, but they’re used for different reasons. ZzzQuil products are made to help with sleep and often contain ingredients like melatonin or antihistamines that cause drowsiness. NyQuil products are made to treat cold and flu symptoms and usually contain a mix of ingredients for congestion, cough, pain, fever, and runny nose. Check with your pharmacist or primary care provider if you have questions comparing the two.

Risks and warnings for ZzzQuil (diphenhydramine)

ZzzQuil (diphenhydramine) can cause some serious health issues. This risk may be even higher for certain groups. If this worries you, talk to your doctor or pharmacist about other options.

Sleepiness

Risk factors: Drinking alcohol while taking ZzzQuil (diphenhydramine) | Taking other medications that cause sleepiness | Older adult

ZzzQuil (diphenhydramine) can make you very sleepy, which can affect your focus, thinking, and reaction time. It can also raise your risk of falls and accidents. This is more likely if you’re an older adult, drink alcohol, or take other medications that cause drowsiness (e.g., opioids, benzodiazepines, sleep medications). Don’t drive or use machinery until you know how this medication affects you.

Accidental overdose

Risk factors: Taking other products with ZzzQuil (diphenhydramine)

Many over-the-counter (OTC) products contain ZzzQuil (diphenhydramine). It's not safe to use more than one product with this medication at the same time. Taking too much can cause dry eyes or mouth, a fast heartbeat, trouble urinating, fever, or constipation. And high doses can lead to serious problems like confusion, seizures, hallucinations, low blood pressure, or heart rhythm issues.

Worsening of certain health problems

Risk factors: Glaucoma | Enlarged prostate | Breathing problems | Kidney problems

Talk to your primary care provider before taking ZzzQuil (diphenhydramine) if you have glaucoma, an enlarged prostate, breathing problems (like emphysema or bronchitis), or kidney problems. This medication can make these conditions worse and might lead to serious side effects.effects.

ZzzQuil (diphenhydramine) dosage

The average cost for 30 capsules of 25mg of ZzzQuil (diphenhydramine) is $5.05 with a free GoodRx coupon. This is 28.87% off the average retail price of $7.10.

Capsule

Dosage	Quantity	Price as low as	Price per unit
25mg	30 capsules	$5.05	$0.17

Typical dosage for ZzzQuil (diphenhydramine)

ZzzQuil (diphenhydramine) is available as a pill or a liquid.

Age 12 years and older: The typical dose is 50 mg by mouth once nightly at bedtime.
Age under 12 years old: Don't use. Ask your child's pediatrician.

How much does ZzzQuil (diphenhydramine) cost?

To access savings, use a GoodRx coupon and pay just a fraction of the retail price.

Zzzquil (brand)

GoodRx lowest price

$5.05

(save 72.69%)

ZzzQuil (diphenhydramine) (generic)

GoodRx lowest price

$5.05

(save 28.87%)

View prices and coupons

What are alternatives to ZzzQuil (diphenhydramine)?

There are a number of medications that your doctor can prescribe in place of ZzzQuil (diphenhydramine). Compare a few possible alternatives below.

ZzzQuil (diphenhydramine)

Used for:

Occasional trouble sleeping - people 12 years and older

$5.05Lowest GoodRx priceView prices

Diphenhydramine

Used for:

Short-term relief of allergy or common cold symptoms (runny nose, sneezing, itchy nose or throat, and itchy or watery eyes) - people 6 years and older
Occasional trouble sleeping - people 12 years and older

$4.09Lowest GoodRx priceView prices

Doxylamine (Unisom SleepTabs)

Used for: