Doxylamine in Unisom and Nyquil Not Recommended for Insomnia Treatment

Drug Causes Sleepiness With Potential Tolerance and Other Side Effects

In This Article

Doxylamine is a sleep aid found in over-the-counter products such as Unisom and Nyquil. It's sometimes taken to treat insomnia.

Like the related medication diphenhydramine, doxylamine does not require a prescription. That doesn't mean it doesn't come with potential side effects, though. Before taking doxylamine, you should learn how well it works and what problems it can cause.

Common Side Effects of Using Doxylamine for Insomnia
Verywell / Jessica Olah 


Doxylamine is an antihistamine, meaning that it treats allergies. It's also used for nighttime cold symptoms. Causing drowsiness is considered a side effect, but it can be a useful one for some people who need help getting to sleep or staying asleep. It shouldn't be used for more than two weeks to treat insomnia.

How It Works

Like many sleeping pills, doxylamine affects neurotransmittersspecialized chemical messengers that send signals between brain and nerve cells (neurons). More specifically, it blocks receptors that allow the neurotransmitter histamine to affect a neuron. This causes you to get sleepy.

Doxylamine works centrally (within the central nervous system) and elsewhere in the body to sedate you.

Who Should Not Use It

Age Restrictions: Young children under 2 years of age should not use doxylamine. Children under 6 and elderly patients shouldn't use it without a doctor's advice.

Breastfeeding: According to a National Institutes of Health publication, small, occasional doses shouldn't cause problems with breastfed babies. However, larger doses or long-term use may cause drowsiness, irritability, and colicky symptoms in babies. It may also lower your milk supply.

Other Conditions: People with many conditions should be cautious about doxylamine as it may cause problems or drug interactions. These conditions include:

  • Glaucoma
  • Hyperthyroidism
  • Heart disease
  • High blood pressure (hypertension)
  • Asthma
  • Chronic obstructive pulmonary disease (COPD)
  • Pneumonia
  • Peptic ulcer disease
  • Prostate enlargement
  • Liver disease
  • Bowel or bladder obstruction

If you're concerned about whether you may have problems using doxylamine, you should first consult with your doctor. Negative drug interactions are a risk, especially with other medications that affect the brain, so be sure to review your medications with your doctor or pharmacist before starting to use doxylamine.

Side Effects

The list of potential side effects for any drug can be quite long, and doxylamine is no exception. Although you likely wouldn't experience most side effects, and may not have any at all, some that occur commonly with doxylamine include:

  • Dizziness
  • Loss of coordination
  • Headache
  • Stomach pain
  • Thick lung secretions
  • Dry mouth or nose
  • Hyperactivity
  • Constipation
  • Difficulty urinating
  • Low blood pressure
  • Blurred or double vision
  • Rapid or irregular heart rate
  • Sensitivity to light
  • Sweating
  • Erectile dysfunction

Potential Serious Reactions

While they're rare, serious side effects can result from the use of doxylamine, including:

  • Severe allergic reaction, including difficulty breathing (anaphylaxis)
  • Low blood cell counts (agranulocytosis, anemia, thrombocytopenia, and leukopenia)
  • Abnormal heart rhythms or altered heart rate
  • Seizures
  • Toxic psychosis
  • Inner ear problems (acute labyrinthitis)
  • Hallucinations
  • Confusion or delirium
  • Low blood pressure

What You Should Know

As an over-the-counter medication, the risks are thought to be slightly lower than with prescription medications that require more careful monitoring. No routine tests are recommended with its use.

Ultimately, doxylamine is not the best option if you are considering taking sleeping pills; there are a number of other choices that are better suited to aiding sleep.

To take a medication for its side effect—in this case, sleepiness—is not recommended.

Doxylamine doesn't promote sleep in the same way as prescription hypnotic medications, such as benzodiazepine and non-benzodiazepine medications. Doxylamine may ultimately lead to further sleep disruption, including worsened insomnia, or even dependence.

If you have any questions or concerns, you can use our Doctor Discussion Guide below to start that conversation with your doctor.

Insomnia Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

Doctor Discussion Guide Man

A Word From Verywell

If you experience any difficulties when taking this drug, you should be in close contact with your primary health provider. If you wish to pursue preferred treatments for insomnia, you should likewise make an appointment and discuss the better prescription options that are available. Effective treatment may include medications, learning better sleep habits, or cognitive behavioral therapy for insomnia (CBTI).

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Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Krystal AD, Richelson E, Roth T. Review of the histamine system and the clinical effects of Hi antagonists: basis for a noew model for understanding the effects of insomnia medications. Sleep Med Rev. 2013;17(4):263-272. doi:10.1016/j.smrv.2012.08.001

  2. Drugs and Lactation Database. Doxylamine. Bethesda, MD: National Library of Medicine (US). Updated December 3, 2018.

  3. MedlinePlus. Doxylamine. Updated February 18, 2020.

Additional Reading
  • "Doxylamine." Epocrates Rx Pro. Version 16.3, 2016. Epocrates, Inc. San Mateo, California.
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