Bottom line

Zzzquil is expensive for what it is, and not very effective for many people. Its active ingredient is diphenydramine, which is a common antihistamine found in many less expensive products (such as Benadryl). The vast majority of studies suggest not using antihistamines for sleep.

What is Zzzquil, and how’s it supposed to work?

Basically, they just took Nyquil, eliminated all the active ingredients, swapped in a different antihistamine, then heavily marketed the resulting Zzzquil as a sleep aid. Lame! But possibly effective for making money.

There are advantages though, safety-wise. Without acetaminophen, the risk of an overdose goes way down. And without dextromethorphan, the chances of using it recreationally or to cook up meth also go away.

Here’s the way diphenydramine is supposed to help sleep: H1 histamine receptors help keep you awake, so theoretically, blocking those receptors using an antihistamine like diphenydramine may help you fall asleep. But research suggests that anthistamines aren’t actually that effective for sleep, mostly due to quickly-developing tolerance to any sleep benefits.

Are there any downsides of trying Zzzquil for sleep?

Why yes, there are many in fact.

Side effects are rather common. Some people actually have a harder time falling asleep after taking antihistamines. Dry mouth is common, as well as a feeling like you have to pee. Which, as you can guess, can be unhelpful for trying to get to sleep.

Another issue is that you often need higher and higher levels of an antihistamine to fall asleep. This tolerance can make antihistamine use unwise for more than a few days.

In case you needed another reason not to take Zzzquil, here are more: antihistamines can reduce sleep quality, making you more tired the next day. And because older people are more susceptible to antihistamine side effects stemming from anticholinergic properties, they should avoid them.