How Much ZzzQuil Can You Safely Take?

In our latest question and answer, our pharmacist discusses the dosing recommendations for ZzzQuil Sleep Aid.

Jan 09, 2018

Kurt asked

I just purchased ZzzQuil to help get some sleep. It says to only take one cap full but could I double dose without running into any issues? I’m about 350 lbs.


ZzzQuil Nighttime Sleep Aid is a product manufactured by Vicks in multiple formulations including:

  • ZzzQuil Liquicaps
  • ZzzQuil Warming Berry Liquid
  • ZzzQuil Calming Vanilla Cherry Liquid
  • ZzzQuil Soothing Mango Berry Alcohol Free Liquid

All ZzzQuil products contain the sedating antihistamine diphenhydramine, the active ingredient in Benadryl. While the onset of action of diphenhydramine is about 30 minutes, the maximum sedative effects begin 1-3 hours after taking the medication. For most, the duration of action ranges from 4—6 hours.

Liquid ZzzQuil Dosage Recommendations

All liquid formulations of contain 25 mg of diphenhydramine per 15 ml (one tablespoon). Per the manufacturer, the recommended dose is 30 ml (two tablespoonfuls) at bedtime, which equates to 50 mg of diphenhydramine. When using diphenhydramine as a sleep aid, single doses should not exceed 50 mg per dose. 

ZzzQuil Liquicaps Dosage Recommendations
Each liquicap of ZzzQuil contains 25 mg of diphenhydramine. The recommended dose at bedtime is 2 liquicaps at bedtime, for a total dose of 50 mg.
Additional Information
Diphenhydramine, the active ingredient in ZzzQuil is often used for the treatment of allergies and allergic reactions. in these situations, the dosage recommendation is different versus use as a sleep aid. Doses up to 100 mg have been safely used for the treatment of allergic reactions. However, as ZzzQuil is purely indicated for the use as a sleep aid, dosages should not exceed 50 mg (30 ml). Doses above this have the risk of causing a "hangover" effect the next morning and more rarely, paradoxical reactions such as insomnia and restlessness.
While doses over 50 mg of diphenhydramine (e.g. 100 mg) typically won't cause any toxicity or overdose issues, it is not recommended for the treatment of sleep.It likely won't increase the effectiveness of the medication and may increase the risk of side effects.

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