ZzzQuil Nighttime Sleep Aid Review

photo of zzzquil sleep aid box and pills

I recently tested the non-prescription sleep aid ZzzQuil for several nights to see if it would help me sleep better.

It’s made by Vicks, who also make Benadryl. Benadryl is sold as a medication for allergies and essentially has the same ingredients.

So depending on your point of view, it kind of looks like where drowsiness is seen as a side-effect of Benadryl by the manufacturer, it’s repackaged as a desirable effect in ZzzQuil.

Note that ZzzQuil Nighttime Sleep Aid is not the same as ZzzQuil Pure Zzzs. The version I’m talking about in this article contains an anti-histamine. The one linked above has melatonin and herbal ingredients instead.

My experience

photo of one of the zzzquil liquicaps that I took

I took just one ZzzQuil liquicap to test it on the first night, rather than the recommended dosage of two caps. I noticed that the liquicap is smaller than the standard white pills that some brands use, so it’s a bit easier to swallow.

I’d actually tried to go to sleep naturally at first, but was struggling to sleep because of the heat. So I got up around midnight, took it and tried to fall asleep again. Interestingly, my sleep tracker data for that night showed that I was in and out of light sleep until around 30 minutes after taking it.

And after that, I slept pretty much straight through the night. I apparently got 7 hours 20 minutes sleep, which was the first time I’d managed 7 hours in a while.

Fuzzy head

When I woke up, I had a slightly fuzzy head. Nothing too serious though, and I felt back to normal around an hour later.

Night 2

I decided to take the full dosage this time and then lay in bed reading to see if I noticed a sedative effect.

There was no overwhelming drowsiness, but after around 40 minutes of reading, I felt a little sleepy and turned the light off. I had a couple of wakings in the night, but they were only a few minutes long. So I again had a pretty decent night’s sleep.

My sleep tracker also recorded that I got more REM and deep sleep than normal. And although you can’t really rely 100% on a sleep tracker for accuracy, it’s interesting that it picked this up.

The hangover effect

Compared to the mild cloudy head of the previous morning, there was a much more noticeable hangover effect. Whether it was the full dosage, two nights in a row taking the ZzzQuil, or something unrelated, I’ll never know.

But I woke with a headache, a heavy feeling in my eyes, and a cloudiness to my thinking that would take a couple of hours to completely disappear.

Night 3

I took the full dosage again and had a very similar experience as night 2. I did wake several times, but never for more than 5 minutes.

And the fuzzy head once again appeared in the morning, taking a fair while to clear up completely.

Night 4

I decided to try just the single dosage again on the final night of my tests. I didn’t sleep as well as the previous nights, taking a little longer to go to sleep, and waking up for longer periods in the night. I had a slightly foggy head, but not nearly as much as on nights 2 and 3.

My conclusion

Both my manual sleep diary and sleep tracker suggest that the ZzzQuil increased my total sleep time – especially with the full dosage. There also appeared to be a difference in how often I woke in the night compared to the week before, and in how long it took me to fall asleep after waking.

And comparatively, taking 2 liquicaps may have led to shorter wakings than just 1 cap. However, there was also a big difference in the hangover effect according to the dosage. I think if I were to take ZzzQuil again, I’d stick with 25 mg. Even if the full 50 mg keeps me asleep for longer, the next day effects aren’t worth it in my opinion.

Further information

ZzzQuil Ingredients

photo showing the label of a box of zzzquil with the ingredients listed as diphenhydramine 25mg

Active ingredient

There’s one active ingredient – 25 mg diphenhydramine HCL (hydrochloride)

Inactive ingredients

  • FD&C Blue No. 1
  • FD&C Red No. 40
  • Gelatin
  • Glycerin
  • Pharmaceutical ink
  • Polyethylene glycol
  • Purified water
  • Sorbitol sorbitan solution


The instructions tell you to take 2 liquicaps at bedtime if you’re an adult or child 12 years and over. That means a dosage of 50 mg. So if you prefer, you can take just one to have a milder effect.

Warnings / who shouldn’t use it

ZzzQuil doesn’t come with an extensive patient leaflet. But there are some important warnings on the back of the box:

Do not use

  • Children under 12
  • With any other product that contains diphenhydramine (even for the skin)

Ask a doctor before use if you have

  • A breathing problem, e.g. emphysema or bronchitis
  • Glaucoma
  • Difficulty urinating because of enlargement of the prostate gland

Ask a doctor or pharmacist

  • If you’re taking any other sedatives or tranquilizers

When using Zzzquil

  • Avoid alcoholic beverages

If pregnant or breastfeeding

  • Ask a health professional before use

Side effects

The box doesn’t have any information about side effects. And with no accompanying patient leaflet, I was left to investigate this myself. It has the same active ingredient as several other sleep aids, so there’s plenty of information about the possible side effects of diphenhydramine HCL.

You can also see the full list of possible side effects on the drugs.com diphenhydramine page.

The main ones they highlight for consumers are:

  • Sedation/sleepiness (the aim of using it as a sleep aid!)
  • Dizziness
  • Incoordination
  • Epigastric distress (pain or discomfort in the abdomen)
  • Thickening of bronchial secretions
  • Headache
  • Dry mouth

There are several other side effects which are reported as rare on drugs.com, but you might like to check them before taking ZzzQuil.


Drugs.com is also a good source of information about interactions with other medications, of which there are 820 listed at the time of writing. If you’re taking any other drugs, you can search for that specific interaction on their website.

It’s also a good idea to talk to your personal doctor if you’re using any other medication to be sure it’s safe for you.

What others say

I didn’t find any serious articles online from other bloggers or medical writers. However, there are many customer reviews on sites that sell it. At the time of writing, some examples include:

  • Target: 4.1 out of 5 stars (65973 customers)
  • Amazon: 4.4 (1317 customers)
  • Walmart: 4.1 (66548 customers)

I read several hundred of the longer comments and found they follow a similar pattern to many other over the counter sleep aids. Some people say they work wonders, while others report that they did nothing for them.

And there are many people who say ZzzQuil worked, but they had a similar hangover effect as I did in the morning.

Your experience of ZzzQuil

Have you tried it? Did it work for you, or give you any side effects? Please share your experience in the comments below.

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