Drowsiness, Dizziness, and More: 8 NyQuil Side Effects You Should Know About

NyQuil is a popular over-the-counter (OTC) combination cold medication. But NyQuil isn’t just one medication: It’s the brand name for a line of products. While the active ingredients vary between formulations, all NyQuil products contain an antihistamine, such as doxylamine, to help you sleep. Many also contain acetaminophen (a pain reliever) and dextromethorphan (a cough suppressant).

Like other combination cold medications, NyQuil products can help you conveniently treat multiple symptoms at once. But it’s important to consider the risks and side effects of a product before taking it.

Note: In this article, we’ll focus on the side effects of NyQuil Cold and Flu, one of the most popular NyQuil products. This medication contains acetaminophen, dextromethorphan, and doxylamine. Your pharmacist can review the side effects of other NyQuil products with you.

NyQuil side effects at a glance

People often report side effects, like feeling sleepy, with NyQuil. Most of these side effects are mild and go away as the medication wears off. However, some side effects may be more intense for certain groups of people, especially those 65 or older.

Mild NyQuil side effects include:

• Drowsiness or, less commonly, trouble sleeping

• Dizziness

• Constipation

• Nausea

• Headaches

• Nervousness or agitation (usually only for kids)

• Dry mouth

• Blurry vision

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Rare but serious NyQuil side effects include:

• Liver damage

• Higher risk of falls for older adults

• Misuse

• Serious skin reactions

• Excessive sleepiness or dizziness

• Serotonin syndrome

Potentially life-threatening allergic reactions, which are considered an adverse reaction rather than a side effect, can also occur. But they are very rare.

Below, we’ll cover eight of the above NyQuil side effects in more detail.

Good to know: Liquid NyQuil contains 10% alcohol, and each 30 mL dose contains 24 mg of sodium. But NyQuil capsules don’t include either of these inactive ingredients. If you typically try to limit sodium or alcohol, consider taking the oral capsules instead of the liquid.

1. Drowsiness

Drowsiness is a common NyQuil side effect and one of the reasons why people take it. This is mainly due to NyQuil’s doxylamine component. While dextromethorphan can cause drowsiness, it’s not as common.

If you’re 65 or older, you may be more sensitive to drowsiness from NyQuil. In fact, experts recommend that older adults avoid medications that contain doxylamine. The risk of severe drowsiness usually outweighs the benefits of these medications for most people in this age group.

Take NyQuil at bedtime or when you’re able to sleep during the day. You should also avoid activities that require alertness, like driving. Drowsiness related to NyQuil can last for 6 hours or more after taking a dose. The medication can also cause next-day drowsiness.

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You shouldn’t combine NyQuil with other medications or substances that can cause drowsiness, including opioids, sleep medications, or alcohol. Doing so can lead to excessive drowsiness.

2. Dizziness

Dizziness is another common NyQuil side effect. Similar to drowsiness, this is primarily due to the doxylamine in NyQuil. Though, dextromethorphan can also cause dizziness (or lightheadedness). Older adults are more likely to experience this NyQuil side effect.

If you feel dizzy, find a place where you can sit or lie down. And be sure to move slowly and carefully when changing positions, such as from sitting to standing. You may also want to grab onto a sturdy surface when standing.

Dizziness related to NyQuil should resolve on its own once the medication wears off (about 6 hours after a dose). As with drowsiness, avoid taking other medications and substances that cause dizziness or drowsiness with NyQuil. This combination could worsen dizziness.

3. Constipation

Constipation is another NyQuil side effect caused by doxylamine. Doxylamine blocks the effects of a chemical called acetylcholine. This chemical helps with a lot of bodily functions, including the movement of food through the digestive tract. Blocking acetylcholine can lead to constipation because this process is slowed down.

Constipation from NyQuil should resolve once you stop taking the medication. Staying well hydrated and slowly increasing the amount of fiber in your diet can help relieve constipation. You can also ask a healthcare professional whether a gentle laxative or stool softener would be OK for you.

Let a healthcare professional know if you have constipation that is severe or doesn’t seem to get better within a few days of stopping NyQuil.

4. Nausea

While it’s not common, some people experience nausea while taking NyQuil. This is most likely due to the dextromethorphan in the medication. It’s also possible for the alcohol in liquid NyQuil to cause nausea.

Nausea related to NyQuil should resolve as the medication wears off. Try taking NyQuil with food if the medication upsets your stomach. Drinking more fluids and opting for smaller, more frequent meals throughout the day can also help. If you’ve been taking regular liquid NyQuil, try switching to the capsules or an alcohol-free liquid version.

Seek medical help if you have nausea that’s accompanied by symptoms such as stomach pain on your right side or yellowing of the skin or eyes. These could be symptoms of liver damage, a rare but serious NyQuil side effect.

5. Headaches

It’s possible for NyQuil to cause headaches. Though, keep in mind that headaches are also a symptom of colds. If you have headaches related to NyQuil, they should clear up once the medication wears off.

In the meantime, here are some tips you can try to relieve your headaches:

• Get extra rest whenever you can.

• Be sure you’re drinking enough water or other fluids.

• Avoid foods and drinks that can trigger or worsen headaches, like chocolate and alcohol.

If you want to try an OTC headache medication, ask your pharmacist which one would be best for you. Like NyQuil, many OTC headache medications contain acetaminophen. Taking one of these medications with NyQuil could result in taking much acetaminophen.

6. Higher risk of falls in older adults

As mentioned, experts recommend that adults 65 and older avoid NyQuil because it contains doxylamine. First-generation antihistamines like doxylamine raise the risk of falls in older adults. And falls can result in broken bones, hospitalizations, and death in this age group.

If you’re 65 or older, your pharmacist can help recommend an alternative OTC cold medication that doesn’t contain an antihistamine.

7. Liver damage

In very rare cases, the acetaminophen in NyQuil can cause or contribute to liver damage. This usually happens because someone takes too much acetaminophen. Taking NyQuil as directed and only when needed helps lower the risk of liver damage.

Acetaminophen is included in hundreds of prescription and OTC medications. While taking NyQuil, be sure to check the labels of your other medications to see if they contain acetaminophen. The maximum daily dose of acetaminophen for most adults is 4,000 mg from all sources in 24 hours.

If you have a history of liver problems, ask a healthcare professional before taking NyQuil. You may need to avoid NyQuil completely or take a lower dosage.

Symptoms of liver damage can include:

• Nausea or vomiting

• Fatigue

• Stomach pain on the right side

• Dark-colored urine

• Yellowing of the skin or eyes (jaundice)

If you have symptoms of liver damage, seek medical help right away. And if you think that you may have taken too much acetaminophen, go to an ER. Acetaminophen overdoses can be fatal if not treated quickly enough.

8. Misuse

As mentioned above, NyQuil contains dextromethorphan. There is a risk of misuse with cough syrups that contain this cough suppressant, particularly among teens.

At high dosages, dextromethorphan can provide a “high” sensation. But it can also cause serious side effects, such as hallucinations (seeing things others don’t), seizures, and abnormal heart rhythms. In the most severe cases, people have experienced trouble breathing and coma.

Taking the recommended NyQuil dosage helps lower the risk of these serious side effects.

If you or someone you know struggles with substance use, help is available. Call SAMHSA’s National Helpline at 1-800-662-4357 to learn about resources in your area.

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Written by:

Dima Cheetany, PharmD

Dima Cheetany is a clinical pharmacist, clinical instructor, and academic detailer at the University of Illinois at Chicago. She graduated with her Doctor of Pharmacy from Roosevelt University College of Pharmacy in 2016.

Edited by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

Reviewed by:

Jennifer Gershman, PharmD, CPh, PACS

Jennifer Gershman, PharmD, is a licensed pharmacist in Florida. She has worked in the pharmacy industry for more than 15 years and is currently a medical writer.

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