Can NyQuil Cause Memory Loss?

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When you get a nasty cold, you might pop some NyQuil before bed and think nothing of it. But some people take over-the-counter (OTC) antihistamine-containing sleep aids (i.e. NyQuil) to help them fall asleep even when they're not sick—a strategy that might not sound very risky at first, but can actually be more detrimental than you may think.

Take Whitney Cummings, for example: On a recent episode of her podcast Good For You, the comedian explained that she's dealing with a coyote problem in her yard (LA problems), so she regularly checks the footage from a security camera that covers the area.

But one day, she saw some footage that surprised her. See, Cummings said she'd gotten into the habit of taking NyQuil before bed purely to help her sleep, and the video she watched showed her walking into her yard in the middle of the night and peeing into some bushes. The most troubling part? She said she had no recollection of it happening—and it all went down after she'd taken NyQuil. (Note: It's not clear how much NyQuil Cummings took, but the recommended dose for adults is 30 mL, or 2 tablespoons, every six hours, and you shouldn't exceed four doses in one day.)

While Cummings said she found the situation hilarious, she also acknowledged that it was a bit scary... and that maybe it was time to give up her NyQuil habit.

But is what happened to Cummings something that people who take OTC antihistamine-containing sleep aids should be worried about? Or is Cummings' experience more of a one-off situation? Here, doctors explain what can happen when you take these types of medications regularly, plus how to use them safely.

How do OTC sleep aids work?

Before we dive in, it's important to define "OTC sleep aids".

There are natural OTC sleep aids—such as melatonin and Valerian root—and then there are antihistamine-containing OTC sleep aids. The latter fall into two categories: pain-relieving and non-pain-relieving. The difference between the two? Medications like NyQuil, AdvilPM, and Tylenol Cold and Cough Nighttime include pain relievers (such as acetaminophen or ibuprofen) to help you feel better when you have a cold or the flu, but they also contain antihistamines. Medications marketed as "nighttime sleep aids," like ZzzQuil, just contain antihistamines.

Both types of antihistamine-containing OTC sleep aids make use of the drowsy side effects associated with certain types of antihistamines, which are also used to treat allergies (think: Benadryl). As the name implies, antihistamines work against histamine, a chemical in your body, which has many functions, one of which is to keep your brain awake and alert. So when histamine gets blocked, you feel more tired, explains Ramzi Yacoub, Pharm.D., a pharmacist and SingleCare's chief pharmacy officer. The most common antihistamines found in OTC sleep aids are diphenhydramine (found in AdvilPM) and doxylamine (found in NyQuil and Tylenol Cold and Cough Nighttime), he adds.

Antihistamine-containing OTC sleep aids frequently have side effects.

Sleepwalking is a pretty well-documented side effect of prescription sleep medications like Ambien. While some might call what happened to Cummings "sleepwalking," that's actually not the most accurate way to characterize the side effects described by the comedian, says Stephanie Stahl, M.D., a sleep medicine physician at Indiana University Health. "While sleepwalking is not commonly reported with [antihistamine-containing] OTC sleep aids, these medications can cause sedation, confusion, memory lapses, and sleep fragmentation, which can increase the risk of sleepwalking or nocturnal wandering," she explains.

You may recognize this blackout effect from another common substance: alcohol. That's because anything sedative—including both alcohol and antihistamine-containing sleep aids—can cause "disorders of confusional arousal," notes Alex Dimitriu, M.D., founder of Menlo Park Psychiatry & Sleep Medicine, who is double board-certified in psychiatry and sleep medicine. "What this term means is that people are half-awake, half-asleep, and generally cannot remember what happened," he explains. So... exactly what happened to Cummings. "When the brain is half-asleep, memory tends to go," he adds.

Another potential (and ironic) side effect of some antihistamine-containing OTC sleep aids is less-than-great sleep. "There is some concern that diphenhydramine may also negatively impact sleep by reducing REM sleep (or dream sleep)," says Dr. Dimitriu. Lack of REM sleep can affect your memory, mood, cognitive performance, and even cell regeneration, so this can be pretty problematic.

Antihistamine-containing OTC sleep aids often don't actually help you sleep longer either, notes Dr. Stahl. "On average, people who take these medications sleep only a little longer by approximately 10 minutes," she explains. "Additionally, most people build up a tolerance and physical dependence in just a few days of taking these medications." While Dr. Stahl says antihistamine-containing OTC sleep aids aren't considered an "addictive" substance, it's possible to get into the habit of needing them to sleep if they're overused, she explains. And over time, they can become less effective at helping you snooze since your body easily builds up a tolerance to the medication, making your sleepless situation worse. So it's one thing to take a dose of NyQuil when you're sick and having a hard time sleeping. But taking an antihistamine-containing OTC sleep aid just to sleep better is unlikely to produce the desired result, says Dr. Stahl.

Other side effects of antihistamine-containing OTC sleep aids can include dry mouth, constipation, blurry vision, and balance and coordination problems, among others. "These medications can also worsen other medical problems and sleep disorders, such as restless legs syndrome," notes Dr. Stahl.

And while antihistamines, in general, are a fairly common medication, there can be potential downsides to taking them regularly long-term. For example, research published in JAMA Internal Medicine found that people who took a standard dose of "first-generation antihistamines" (which can include diphenhydramine—the one found in AdvilPM—among other types of antihistamines) approximately once per week over a 10-year period were at an increased risk of dementia. "Just because something is available OTC does not mean that it is safe or effective," says Dr. Stahl.

How will you know if an antihistamine-containing OTC sleep aid is affecting your memory?

One detail that made Cummings' story so scary was that it seems she'd never have found out it happened if she hadn't checked her security camera. After all, not everyone has security camera coverage all over their house. Luckily, though, there are some other smart ways to keep an eye on any unusual nighttime activity if you're taking an antihistamine-containing OTC sleep aid.

"Apps that record sounds all night are the second best thing to cameras for people who want to be sure they are not doing anything strange," suggests Dr. Dimitriu. "Activity trackers and smartwatches may also provide clues to excessive activity at night." Plus, most people grab their phones when they wake up, he notes. So, looking at texts, internet activity, and calls might also be helpful, he says. (Related: 10 Free Apps to Help You Sleep Better Tonight)

The Right Way to Take Antihistamine-Containing OTC Sleep Aids

Experts agree that taking an OTC antihistamine-containing sleep aid like NyQuil every night isn't a great idea. But if you need help sleeping occasionally, here's how to use OTC antihistamine-containing sleep aids safely.

Tell your doctor if you're using them. One of the biggest reasons to do this is because OTC antihistamine-containing sleep aids can interact with other substances you might commonly use—like alcohol and marijuana, says Dr. Stahl. "They also interact with many other medications, including antidepressants," she adds. "Before starting any OTC medication, check with your doctor to determine if it may interact with your other medications or worsen other medical problems and if a different treatment is better."

Never drive after taking them. "[OTC antihistamine-containing sleep aids] increase the risk of car accidents and may cause more driving impairment than a blood alcohol level of 0.1 percent," explains Dr. Stahl. So, hands off the wheel post-NyQuil. If you're concerned about sleepwalking or blacking out like Cummings, put your keys in a safe place out of reach until morning.

Don't rely on them long-term. OTC antihistamine-containing sleep aids are meant to be used for the occasional night when you're feeling under the weather and can't fall asleep, says Yacoub. "If you are having trouble sleeping for an extended period, I would recommend seeing your physician who can evaluate this further," he notes.

Practice good sleep hygiene. "This is ultimately what helps people sleep the best, without any medication," says Dr. Dimitriu. Practicing regular bed and wake times, avoiding screens before bed, and getting morning sunlight can all go a long way to promoting good sleep hygiene, he notes.

If you're dealing with insomnia, consider other treatments. "Rather than masking your sleep problems with medications, fixing the root of the problem is best," explains Dr. Stahl. "Cognitive-behavioral therapy for insomnia is the recommended frontline treatment for chronic insomnia, not a medication."