Are Antihistamines Safe for Sleep?

If you've ever taken Benadryl, ZzzQuil, or Tylenol PM to help you sleep, you're not alone. Antihistamines are one of the most common over-the-counter options people reach for when they can't fall asleep.

They're easy to find, don't require a prescription, and they work—at least in the short term. But using antihistamines as a regular sleep aid raises some questions. Are they actually meant for sleep? What happens if you use them often? And are there risks you should know about?

Here's a closer look at what antihistamines do, why they make you drowsy, and whether they're a safe choice for ongoing sleep problems.

What are antihistamines?

Antihistamines are medications designed to block histamine, a chemical your body releases during allergic reactions. When you have allergies, histamine causes symptoms like sneezing, itching, a runny nose, and watery eyes. Antihistamines reduce these symptoms by preventing histamine from binding to receptors in your body.

There are two main types:

• First-generation antihistamines (diphenhydramine, doxylamine) cross into the brain and cause drowsiness as a side effect. These are the ones commonly used for sleep.

• Second-generation antihistamines (loratadine, cetirizine) are designed to work without causing as much drowsiness. They're not typically used as sleep aids.

When people talk about using antihistamines for sleep, they're almost always referring to first-generation antihistamines, particularly diphenhydramine.

Why do antihistamines make you sleepy?

Histamine doesn't just trigger allergy symptoms. It also plays a role in wakefulness. Your brain uses histamine to help keep you awake during the day.

When you take a first-generation antihistamine like diphenhydramine, it crosses the blood-brain barrier and blocks histamine receptors in your brain. This reduces wakefulness and makes you feel drowsy.

This sedating effect is a side effect, not the intended purpose of the medication. Diphenhydramine was developed to treat allergies, not insomnia. The drowsiness just happened to be useful for people who had trouble sleeping.

Most OTC sleep aids, including ZzzQuil, Unisom SleepTabs, and the "PM" versions of pain relievers like Tylenol PM and Advil PM, contain diphenhydramine as their active ingredient. You're essentially taking an allergy medication for its side effects.

Are antihistamines effective for sleep?

For occasional use, yes. Diphenhydramine can help you fall asleep faster. Studies show it reduces the time it takes to fall asleep and may modestly increase total sleep time.

However, the quality of sleep you get may not be as good as natural sleep. The same study suggests that antihistamines can reduce the amount of time spent in REM sleep, which is important for memory, learning, and emotional regulation.

There's also the issue of next-day effects. Many people report feeling groggy, foggy, or sluggish the morning after taking diphenhydramine. This "hangover" effect can last well into the next day, affecting concentration and performance.

For short-term, occasional use—like adjusting to jet lag or getting through a stressful night—antihistamines can be helpful. For ongoing sleep problems, they're less ideal.

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What happens with regular use?

One of the biggest issues with using antihistamines for sleep is tolerance. Your body adapts to the medication over time, and the sedating effect becomes less pronounced.

Many people find that after a week or two of regular use, the same dose doesn't work as well. This can lead to taking higher doses to achieve the same effect, which increases the risk of side effects.

Stopping antihistamines after regular use can also cause rebound insomnia. Your sleep may temporarily get worse before it normalizes, which can make it tempting to keep taking the medication.

This pattern—tolerance, dose escalation, and rebound effects—is one reason sleep specialists generally don't recommend antihistamines for chronic insomnia.

What are the side effects?

Diphenhydramine and other first-generation antihistamines come with a range of potential side effects.

Common side effects include:

• Next-day drowsiness and grogginess

• Dry mouth

• Blurred vision

• Constipation

• Urinary retention (difficulty urinating)

• Dizziness

• Confusion, especially in older adults

The anticholinergic effect:

Diphenhydramine has anticholinergic properties, meaning it blocks acetylcholine, another neurotransmitter in your brain. This is what causes side effects like dry mouth, constipation, and blurred vision.

The anticholinergic effect is also concerning from a cognitive standpoint. Acetylcholine plays a role in memory and thinking. Blocking it, especially in older adults, can cause confusion, cognitive impairment, and increased fall risk.

Is there a link between antihistamines and dementia?

This is where things get more serious.

Several studies have looked at long-term use of anticholinergic medications, including diphenhydramine, and the risk of dementia. A widely cited 2015 study published in JAMA Internal Medicine found that cumulative use of anticholinergic medications was associated with an increased risk of dementia in older adults.

The study found that people who used anticholinergic drugs for three years or more had a significantly higher risk of developing dementia compared to those who didn't use them. Diphenhydramine was specifically named as one of the medications studied.

It's important to note that this research shows an association, not definitive proof of cause and effect. Other factors could be involved. But the findings have raised enough concern that many healthcare providers now recommend limiting or avoiding long-term anticholinergic use in older adults.

The American Geriatrics Society includes diphenhydramine on the Beers Criteria, a list of medications that are potentially inappropriate for people 65 and older due to safety concerns.

Also Read: Insomnia and Sleep Meds Linked with Dementia in New Study—Here’s an Alternative

Who should avoid antihistamines for sleep?

Certain groups should be particularly cautious about using diphenhydramine and similar medications:

• Older adults (65+): Higher risk of confusion, cognitive effects, falls, and urinary retention. The risks generally outweigh the benefits for this group.

• People with glaucoma: Anticholinergic effects can increase eye pressure.

• People with urinary retention or enlarged prostate: Can worsen difficulty urinating.

• People with certain heart conditions: Can affect heart rhythm in some cases.

• People taking other sedating medications: Combining sedatives increases the risk of excessive drowsiness and impaired coordination.

• Pregnant or breastfeeding women: Should consult a doctor before use.

If you fall into any of these categories, talk to a healthcare provider before using antihistamines for sleep.

What do sleep experts recommend instead?

For occasional sleepless nights, antihistamines are generally considered safe for most adults. But for ongoing sleep problems, there are better approaches.

Cognitive behavioral therapy for insomnia (CBT-I): This is the first-line treatment recommended by sleep specialists for chronic insomnia. It addresses the thoughts and behaviors that perpetuate sleep problems, and research shows it's more effective than medication in the long run.

Sleep hygiene improvements: Consistent sleep schedules, a cool and dark bedroom, limiting caffeine and alcohol, and establishing a wind-down routine can all make a difference.

Addressing underlying causes: If stress, anxiety, or a medical condition is driving your sleep problems, treating the root cause is more effective than masking the symptom with medication.

Natural sleep aid: If you want something to help you relax without the side effects of antihistamines, natural alternatives exist. Sip2Sleep® is a melatonin-free option made with Montmorency tart cherry extract and Rafuma Leaf (Venetron®) that supports sleep quality and helps reduce anxiety, without the next-day grogginess or cognitive concerns associated with diphenhydramine.

So, are antihistamines safe for sleep?

For occasional, short-term use in otherwise healthy adults, antihistamines are generally safe. They can help you get through a rough night or reset your sleep after travel.

For regular use, the picture is less clear. Tolerance builds quickly, next-day drowsiness is common, and there are real concerns about cognitive effects, especially with long-term use or in older adults.

If you find yourself reaching for diphenhydramine or ZzzQuil most nights, it's worth reconsidering. You may be masking a sleep problem that would respond better to other approaches, and you may be taking on risks that aren't necessary.

Talk to a doctor if your sleep problems persist. There are safer, more effective ways to address ongoing insomnia than relying on a medication that was never designed for that purpose.

References: 

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