How Long Does Nyquil Last

How long does Nyquil last?

You don’t want to feel groggy when you wake up in the morning after you’ve taken a dose of Nyquil, especially if you have to drive to work or operate machineries, so knowing how long Nyquil lasts could help you know how to take the drug and avoid feeling hungover the next morning.

Also, you may be interested in knowing how long Nyquil lasts regarding its effect on relieving your symptoms, to know how long you’ll feel relieved. So how long does Nyquil last and what makes it last as long as it does? Keep reading, and in a bit, you’ll learn all you need to know about Nyquil, including how long it lasts in your system.

About Nyquil 

Before we get to how long Nyquil lasts, let’s briefly talk about some features of the drug.

Nyquil is a common over-the-counter drug specially made to relieve nighttime cold and flu symptoms such as runny nose, cough, sore throat, headaches, body pains, and sneezing, helping you to sleep better at night. It also helps in relieving symptoms of allergies such as sneezing, rashes, or hives.

Several Nyquil products are available on the market, and they all contain 3 major active ingredients: Acetaminophen, Dextromethorphan, and Doxylamine, however, some forms of Nyquil contain alcohol. Nyquil exists as a caplet and also as a liquid drug.


Nyquil contains:

  • Acetaminophen
  • Dextromethorphan
  • Doxylamine
  • Sodium citrate
  • Citric acid
  • Propylene glycol
  • Polyethylene glycol

How Does Nyquil Work

To know how Nyquil works, let’s consider each of its ingredients and the role they play in relieving cold and flu symptoms.

  • Acetaminophen: This is a pain reliever and a fever reducer. It works by blocking the brain from producing certain chemicals that are responsible for pain and fever.
  • Dextromethorphan: It’s a cough suppressant that works by stopping the part of your brain that sends coughing signals to your body, thereby reducing your urge to want to cough.  
  • Doxylamine succinate: This is an antihistamine that blocks the action of histamine, a chemical your body secretes when you come in contact with something you’re allergic to.
  • Citric acid: Some Nyquil products contain citric acid in small quantities. Citric acid can act as a flu killer.
  • Polyethylene glycol and Propylene glycol: These two ingredients are known as inactive, as they don’t contribute to the effect of the drug, however, they help in maintaining the texture of the drug.
How Long Does Nyquil Last
How Long Does Nyquil Last?

Side Effects

Some of the common side effects of Nyquil include:

  • Dizziness
  • Drowsiness
  • Stomach upset
  • Anxiety
  • Fatigue
  • Nausea
  • Vomiting
  • Loss of appetite
  • Constipation 
  • Blurred 
  • Dry throat
  • Hangover

However, sometimes, you may experience serious side effects such as:

  • Hallucination
  • Seizure
  • Trouble urinating
  • Abnormal heartbeat 

This is not the full list of all side effects of Nyquil, but you can consult with your doctor to know about other possible side effects. 

These side effects should disappear after some time, when your body has become adapted to the drug’s effect, but should it persist for long or worsen, let your doctor or pharmacist know immediately, you may need to discontinue the drug.

How Long Does Nyquil Last

Because each of the active ingredients contained in Nyquil has different half-lives, different Nyquil products will have different longevity. Half-life is the amount of time it takes for your body to get rid of half of the drug from your system.

For instance, acetaminophen has a half-life of 2-3 hours, after which it’s gradually flushed out of your system, dextromethorphan has a half-life of 3-6 hours and gets flushed out completely after 11-33 hours, while half of the doxylamine gets flushed out after 10 hours, and the whole takes 2.25 days to completely flush out.

So if you take a Nyquil product like Nyquil Cold & Flu which contains these 3 active ingredients, you could expect it to last for 4-6 hours, however, the effect of doxylamine which makes you feel drowsy will last longer. The effect of doxylamine could last for 3-8 hours, which is the optimum period for a night of healthy sleep, but any longer than that could cause you to feel groggy when you wake up. 

On the other hand, if you take Nyquil products like Nyquil Severe which contains an additional ingredient, Phenylephrine, a nasal decongestant. Nyquil Severe will last for about 4-6 hours without much of the sedating effect like the Nyquil Cold & Flu because phenylephrine has a mild stimulant effect.

Nevertheless, how long Nyquil last also depends on your age, metabolism, body mass, and how you take the drug, hence, it may differ for different individuals. If you take Nyquil with other medications, this can also affect long Nyquil lasts.

Factors That Influence How Long Nyquil Lasts?

Let’s consider how certain factors can affect how long Nyquil can last.

  • Age: Older people tend to be more affected by Nyquil because their metabolism is slower and they tend to have other health issues that can make Nyquil effects last longer.
  • Health Issues: Majorly, this includes health issues that concern your renal, urinary, and hepatic functions. If you have any problem with these functions, you’re likely to have slow metabolism of the drug so it will take longer for the drug to be flushed out of your system, as one of the major routes of drug elimination is through your urine.
  • Body Fat: Doxylamine is a lipophilic substance, hence, if you have a higher fat percentage, Nyquil will last longer in your system than it would in someone who has a lesser fat percentage.
  • Other Medication: Certain medications can interact with how long Nyquil can last.

How Long Does Nyquil Last In Your System

Just as we’ve said, how long Nyquil lasts in your system will also depend on your age, metabolism, and how you take the drug, but on average, the effect of each dose of Nyquil will last about 6-8 hours in your system.

After you’ve taken your last dose of the drug, you’ll still feel the effect for hours, but it takes approximately 3 days for the drug to be completely flushed out of your system after your final dose.

How Long Does Nyquil Take To Work

It doesn’t take long before you begin to feel the effect of Nyquil. If you’re taking the liquid form, you’ll feel a warm sensation in your throat the moment you take it, and 10 minutes after you’ve taken the drug, in whatever form, you should begin to notice relief from your symptoms. 

First, you feel your pain relief, and soon after, the side effects kick in, your eyelids become heavy and you begin to feel dizzy and drowsy.

How Long Does It Take Nyquil To Get Out Of Your System?

Approximately, it takes about 65-78 hours to get all the ingredients of Nyquil out of your system, although this may differ depending on which of the Nyquil products have the longest half-life.

How Much Nyquil Can I Take

This depends on what Nyquil product you’re taking. If you’re taking the Nyquil LiquiCaps, 2 of them within every six hours is recommended, but if you’re taking Nyquil Liquid, then you should take about 30 ml every 6 hours.

However, if you’re taking Nyquil pills, you shouldn’t take more than 4 doses within 24 hours, to reduce the chances of suffering severe side effects.

How Long Does Nyquil Last Until It Expires

Every drug has an expiration date depending on the shelf-life of the ingredients used in producing them, the same is applied to Nyquil. How long Nyquil lasts until it expires depends on when it was produced, but you could always find the expiration date on the label or package of the drug.

Other factors such as exposure to heat or cold, can also affect how long Nyquil can last before it expires. If you don’t store the drug as it should be, it’ll likely expire before its expiration date.

When a drug expires, it loses its potency as the ingredients will be degraded and can no longer relieve your symptoms. Although there are no reports of any possible adverse effects from taking Nyquil when it’s expired, regardless, don’t use them beyond their expiration date.

You can find the expiration date of Nyquil stamped at the bottom of the label of the Nyquil bottle, or on the lower part of the box of the Nyquil pill.


Nyquil is an OTC that relieves symptoms of colds, flu, and allergies. It causes some side effects such as drowsiness and dizziness, which can last for about 8 hours, which is why it is best taken at nighttime.

How long Nyquil lasts may also be determined by some factors such as your age, body fat, and metabolism. Regardless of how long it lasts though; you can be sure to have some side effects while taking the drug.

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