Can Nyquil Make You Sleepy?

Nyquil is a widely used over-the-counter remedy formulated to relieve nighttime cold and flu symptoms. One of its antihistamine components, doxylamine succinate, is known to produce drowsiness and promote sleepiness.

Besides helping to reduce fever, nasal congestion, and cough, Nyquil often causes sedation. For that reason, many people find it helpful for inducing sleep.

In this article, we’ll review which Nyquil ingredients are responsible for sleepiness, discuss other possible adverse effects, and cover safety concerns about using Nyquil as a sleep aid.

What ingredients are in Nyquil and which ones can make you drowsy?

There are several Nyquil formulations available, and most of them can induce sleepiness to varying degrees. Typically, drowsiness begins within about 30 minutes after taking Nyquil.

Different Nyquil products may include some or all of the active compounds listed below at differing strengths. Nyquil Severe formulas often include extra active ingredients.

Acetaminophen

Acetaminophen is a common analgesic and antipyretic. It treats symptoms like mild aches and pains, fever, headache, and sore throat, and is generally well tolerated at recommended doses.

Nonetheless, excessive acetaminophen intake can be harmful. Taking more than the safe amount can lead to liver injury. The advised maximum daily dose is 3,000 milligrams (mg), but the margin between a safe dose and a harmful one is relatively small.

Acetaminophen is sold under many trade names, including Tylenol. It appears in these Nyquil products:

• Nyquil Cold and Flu Nighttime Relief (Liquid and LiquiCaps)
• Nyquil Severe Cough, Cold, and Flu Nighttime Relief (Liquids, LiquiCaps, and VapoCool Caplets)
• Nyquil High Blood Pressure Cold and Flu Medicine

Dextromethorphan HBr

Dextromethorphan is a cough suppressant that reduces the neural signals that prompt coughing.

Although side effects are usually mild, they can include:

• drowsiness
• lightheadedness
• restlessness
• gastrointestinal upset

Dextromethorphan HBr is included in the following Nyquil formulations:

• Nyquil Cold and Flu Nighttime Relief (Liquid and LiquiCaps)
• Nyquil Severe Cough, Cold, and Flu Nighttime Relief (Liquids, LiquiCaps, and VapoCool Caplets)
• Nyquil Cough DM and Congestion Medicine (Liquid)
• Nyquil High Blood Pressure Cold and Flu Medicine (Liquid)

Doxylamine succinate

Doxylamine succinate is an antihistamine that blocks histamine, a chemical involved in allergic reactions.

By inhibiting histamine, doxylamine succinate helps ease sneezing, a runny nose, and sinus congestion. It produces notable drowsiness and may also cause headaches and dryness of the sinuses.

Doxylamine succinate is present in these Nyquil products:

• Nyquil Cold and Flu Nighttime Relief (Liquid and LiquiCaps)
• Nyquil Severe Cough, Cold, and Flu Nighttime Relief (Liquids, LiquiCaps, and VapoCool Caplets)
• Nyquil Cough DM and Congestion Medicine (Liquid)
• Nyquil High Blood Pressure Cold and Flu Medicine (Liquid)

Phenylephrine HCl

Phenylephrine HCl is a decongestant that relieves nasal and sinus congestion, such as a runny nose. It does not usually cause drowsiness. Other possible adverse effects include dizziness, headache, and upset stomach.

Phenylephrine HCl is contained in the following Nyquil formulations:

• Nyquil Severe Cough, Cold, and Flu Nighttime Relief (Liquids, LiquiCaps, and VapoCool Caplets)
• Nyquil Cough DM and Congestion Medicine

Is it safe to use Nyquil as a sleep aid?

There are no dedicated studies confirming the safety or effectiveness of Nyquil specifically as a sleep aid.

Some research has looked at the use of antihistamines for sleep. A 2012 literature review suggested that certain first-generation antihistamines might be useful for short-term insomnia.

However, evidence on doxylamine succinate—the sedating antihistamine in Nyquil—is limited. A 2015 review  concluded that there weren’t enough high-quality studies to judge its safety or efficacy as a sleep medication.

Furthermore, doxylamine can produce unwanted effects, including residual daytime sleepiness. Other potential side effects include:

• blurred vision
• headache
• dryness of the mouth, nose, and throat
• nausea
• nasal congestion
• restlessness

Tolerance to doxylamine can develop quickly, meaning its sedative effect may diminish with repeated use.

Because Nyquil contains additional active ingredients that carry their own risks, using a lower-risk nonprescription sleep aid for short-term insomnia may be a safer option.

How to take Nyquil safely

Follow the directions on the product label to use Nyquil safely. Check with your healthcare provider before taking Nyquil if you:

• have an existing medical condition
• are older than 75
• are pregnant or breastfeeding

Because Nyquil causes sedation, you should not combine it with other sleep-promoting agents, such as melatonin. Doing so might produce dangerous sedative effects like shallow breathing.

Avoid drinking alcohol while using Nyquil, since alcohol can amplify drowsiness, dizziness, and other adverse effects. Also, because Nyquil contains acetaminophen, repeatedly combining it with alcohol can raise the risk of liver harm.

Do not take Nyquil together with other products that contain acetaminophen, as that could result in exceeding the advised daily limit.

Other ways to improve sleep

Lifestyle adjustments are often effective for helping you fall asleep and stay asleep. If you struggle with sleep quality, try these strategies:

• Keep a regular sleep routine. Go to bed and wake up at consistent times to reduce disrupted sleep.
• Create a pre-bedtime wind-down. Establish a calming routine before bed—take a warm bath, read, meditate, or listen to relaxing music.
• Limit daytime naps. Keep naps short (20 to 30 minutes) to avoid making nighttime sleep more difficult.
• Optimize your bedroom. Reserve the bedroom for sleep and intimacy. Make it dark, quiet, and cool—ideally between 60 and 67°F (15.6 and 19.4°C).
• Put away screens. Avoid phones, tablets, and computers in the hour before bedtime, as they can stimulate the brain and impede sleep onset.
• Exercise regularly. Physical activity can help you feel sleepy at night. Finish moderate exercise within a few hours of bedtime; vigorous workouts are best earlier in the day.
• Avoid sleep disruptors. Heavy meals, caffeine, and alcohol close to bedtime can interfere with falling and staying asleep.
• Manage stress. Stress can prevent sleep. Try relaxation methods such as breathing exercises, meditation, yoga, or progressive muscle relaxation at night.
• Try an insomnia app. Sleep-tracking and cognitive tools like the U.S. Department of Veterans Affairs Insomnia Coach  app can help monitor and improve sleep patterns.

When to consult a doctor

Occasional trouble sleeping is common. Speak with your clinician if insomnia persists for more than a few weeks or if daytime sleepiness starts to disrupt your work or daily responsibilities.

The bottom line

Nyquil’s active ingredients include acetaminophen, dextromethorphan HBr, doxylamine succinate, and in some products, phenylephrine HCl. Doxylamine succinate is the primary component that causes drowsiness.

There is no strong evidence supporting the use of Nyquil specifically as a sleep aid. If you’re having trouble sleeping, try improving bedtime habits, keeping a consistent sleep schedule, or talking with your healthcare provider about safer sleep options to achieve restorative rest.