7 Unisom Side Effects You Should Know About

Unisom (doxylamine) is an over-the-counter (OTC) antihistamine commonly taken for occasional insomnia — trouble falling asleep or staying asleep. Unisom causes sleepiness by blocking histamine receptors (chemical binding sites) in the brain.

While a good night’s sleep may be a relief, it’s important to know about Unisom's side effects before taking it. For most people, these side effects are mild and resolve on their own. But there are risks to be aware of with Unisom, especially if you’re 65 years or older.

Note: Some Unisom products include active ingredients other than doxylamine. In this article, we’ll focus on those products that only contain doxylamine.

Unisom side effects at a glance

Unisom is generally well tolerated, and its side effects can typically be managed at home or go away on their own. However, side effects can be more severe in certain groups of people.

Examples of common Unisom side effects include:

• Drowsiness, including next-day drowsiness

• Dizziness

• Trouble balancing

• Headache

• Dry mouth

• Constipation

• Blurry vision

Rare but serious Unisom side effects include:

• Sudden changes in vision

• Worsening of certain types of glaucoma

• Higher risk of falls in older adults

• Severe drowsiness or dizziness

• Trouble urinating

Whether you’re experiencing mild Unisom side effects or the symptoms of something more serious, it’s good to know how to manage them. Let’s learn more about seven Unisom side effects.

1. Drowsiness

Unisom is expected to cause drowsiness. That’s the reason most people take it. But it’s also common to experience next-day drowsiness because one dose lasts in the body for several hours. In fact, Unisom is more likely to cause daytime sleepiness than Benadryl (diphenhydramine), another antihistamine commonly taken for sleep.

After taking Unisom, you should avoid activities that require a high level of attention, such as driving. You should also make sure you devote at least 8 hours to sleep. But be aware that you may still feel lingering effects of Unisom even after a full night’s sleep.

In addition, avoid other medications and substances that worsen drowsiness while taking Unisom. Some examples of these include alcohol, opioids, and benzodiazepines. Combining them with Unisom can cause severe drowsiness.

If you have next-day drowsiness with Unisom, consider trying a lower dosage next time. You can also ask your pharmacist or healthcare provider for other OTC sleep aid recommendations.

2. Dizziness

Another common Unisom side effect is dizziness. As with drowsiness, this happens because the medication can pass the blood-brain barrier (a group of cells that protect the brain from certain substances). Medications that pass this barrier can cause brain-related side effects, such as dizziness.

People with certain health conditions like Ménière's disease may be more prone to dizziness. Adults 65 or older may also be more sensitive to this Unisom side effect.

You may not notice dizziness from Unisom while you’re sleeping. But it can be dangerous if you wake up and feel dizzy. Be careful changing positions (such as going from standing to sitting) after taking Unisom and when you first wake up the next morning. If you experience dizziness, find a safe place to sit or lie down to avoid losing your balance.

If your dizziness is severe or doesn’t resolve during the day after you took Unisom, contact your healthcare provider. There may be another cause for your dizziness.

3. Headache

Headaches are another mild but common Unisom side effect. Keep in mind that trouble sleeping can contribute to headaches. So, it can be hard to tell if Unisom is causing this symptom.

Regardless of what’s causing your headache, you can try a few at-home tips for relief:

• Drink more water or other fluids.

• Avoid alcohol, as it can worsen headaches.

• If possible, try exercising or adding more movement into your day.

• Take steps to optimize your sleep routine, such as avoiding screens before bedtime.

• Lower your stress levels through mindfulness, calming activities, or breathing exercises.

Discuss OTC pain relievers with your healthcare provider or pharmacist, such as ibuprofen (Advil, Motrin) or acetaminophen (Tylenol). These can be helpful for occasional headaches and don’t interact with Unisom.

Don’t take pain relievers marketed for nighttime pain relief or labeled with “PM,” such as Tylenol PM (acetaminophen / diphenhydramine). These combination products usually contain an antihistamine similar to what’s in Unisom. Combining antihistamines can worsen side effects.

4. Dry mouth

Dry mouth is another common Unisom side effect. Unisom blocks a chemical called acetylcholine in addition to histamine. Medications that block acetylcholine can cause a group of side effects known as anticholinergic side effects. Dry mouth is one of these.

Dry mouth related to Unisom is typically mild and should go away as the medication’s effects wear off. To help relieve dry mouth at home:

• Suck on ice chips.

• Drink cool liquids.

• Chew sugar-free gum.

• Suck on sugar-free candy.

Contact your healthcare provider if these steps don't work or if your dry mouth doesn’t resolve. This isn’t typical with Unisom and could indicate another cause for your symptoms.

5. Constipation

Constipation is another anticholinergic side effect of Unisom. Blocking acetylcholine slows the movement in your intestines, which can occasionally lead to constipation.

Like many other Unisom side effects, constipation is usually mild. Try drinking more water and eating more fiber to help relieve constipation. Increasing exercise and movement throughout the day may also help.

If these tips don’t work, you can ask your pharmacist about taking an OTC medication for constipation. They can help you choose one that’s safe for you to take. If your constipation doesn’t improve after a few days or becomes severe, contact your healthcare provider.

6. Blurry vision

A less common Unisom side effect is blurry vision. In most cases, blurry vision is just another anticholinergic side effect. It typically clears up after Unisom wears off. Until it does, avoid driving or performing other activities that require focus.

But in some instances, blurry vision can be a warning sign for a serious complication called acute angle-closure glaucoma. Symptoms include blurry vision, eye pain, and halos around bright lights. This is a medical emergency. If left untreated, it can lead to permanent blindness.

People who have narrow-angle glaucoma have the greatest risk of this serious Unisom side effect. But if you have any type of glaucoma, ask your healthcare provider before taking Unisom or other OTC sleep aids.

7. Higher risk of falls

Unisom can raise your risk of falls. Drowsiness and dizziness may contribute to this increased risk. Older adults have a greater risk of falls with Unisom than younger adults. That’s why experts recommend adults age 65 and older avoid taking it.

Many sleeping medications (both OTC and prescription-only) carry extra risks for older adults. If you’re 65 or older, discuss the safest options for treating sleeping difficulties with your care team. Depending on the frequency of your symptoms, they may suggest non-medication insomnia treatments, such as cognitive behavioral therapy.

When should I contact my healthcare provider about Unisom side effects?

Most Unisom side effects, like headache and dry mouth, can be managed at home. They also typically resolve on their own once Unisom wears off. Contact your healthcare provider or pharmacist if side effects seem excessive or remain bothersome.

Seek medical attention immediately if you experience severe dizziness, severe next-day drowsiness, or blurry vision with eye pain. These symptoms can be dangerous, especially if left untreated. They may also increase your risk of falls.

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Written by:

Nicole E. Cieri-Hutcherson, PharmD, BCPS, NCMP

Nicole E. Cieri-Hutcherson, PharmD, BCPS, NCMP, has over a decade of experience as a pharmacist, professor, and researcher. She was a full-time clinical professor in the pharmacy practice department at D’Youville School of Pharmacy before subsequently joining the faculty of the pharmacy practice department at the University at Buffalo School of Pharmacy and Pharmaceutical Sciences.

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:

Austin Ulrich, PharmD, BCACP

Austin Ulrich, PharmD, BCACP, is a board-certified ambulatory care clinical pharmacist. In his early career, he provided direct patient care in a variety of settings, including hospital and community pharmacies, and in a primary care clinic as a clinical pharmacist.

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