Getting a good night’s sleep is paramount to your health. So, when you’re lying awake at 1 A.M. for the third night in a row, you might be tempted to get some rest in any way possible—with whatever’s in your medicine cabinet. Most often, that means an antihistamine that either warns of drowsiness on the box or you anecdotally know makes you conk out. So, how bad is this really? Here’s what you need to know about taking an antihistamine to fall asleep.
The main ingredient in that fast-acting antihistamine is diphenhydramine hydrochloride (DPH).
It’s the active ingredient in Benadryl, an antihistamine meant to treat symptoms of an allergic reaction like itchiness, watery eyes, and sneezing. The sleepy part is really just a side effect listed on the box.
Histamine is a chemical that produces the inflammatory response behind allergy symptoms, but it also plays a key role in promoting wakefulness. (The nature of this relationship is not well understood.) So, along with soothing allergy symptoms, when antihistamines counteract the histamine in your body, they have the side effect of making you feel tired, Rafael Pelayo, M.D., a sleep specialist with the Stanford Sleep Medicine Center, tells SELF.
But this ingredient won’t necessarily knock everyone out. David Rapoport, M.D., director of the Sleep Medicine Research Program and professor of pulmonary and sleep medicine at the Icahn School of Medicine at Mount Sinai, tells SELF that these drugs aren’t very powerful as sleep aids. A 2017 review of the research in the Clinical Practice Guideline for the Pharmacologic Treatment of Chronic Insomnia in Adults examined 46 studies in an attempt to recommend clinical guidelines for treating insomnia. The researchers determined that the evidence behind DPH-based drugs leading to better sleep were “clinically insignificant,” suggesting that people shouldn’t try to use these medications to fall asleep more quickly or stay asleep longer.
However, as Dr. Pelayo points out, how you react to a certain drug is pretty individual, and it’s possible that you might react more strongly due to the placebo effect of taking something you believe will make you sleepy.
Here’s how doctors feel about using DPH to help you fall asleep.
“It’s very attractive to people because it’s an over-the-counter medication,” says Dr. Rapoport. “It’s [seen as] a quick and dirty way to fix your insomnia.”
But, OK, how bad is it in a pinch? DPH is generally very safe and carries a low risk of serious side effects, so it’s not that big a deal if you turn to it to help you drift off every now and then, Dr. Rapoport says. But there are a couple things doctors want you to be aware of first.
“The big problem with this kind of medication is that it lasts a fairly long time in your system,” Dr. Pelayo says. The lingering effect of a standard adult dose (25 to 50 milligrams, i.e., one to two pills or liquid doses) will likely not be incredibly strong, Dr. Rapoport says, but it may be enough to make you feel sleepy or foggy-headed the next morning. Other side effects are mild and can include dry mouth, nose, and throat; dizziness, constipation; headache; and nausea, according to the National Institutes of Health (NIH).
You can also build up a tolerance to DPH fairly quickly. “[Antihistamines] tend to stop working,” Dr. Rapoport says. “The body adapts to them.” With daily use, you may build up a tolerance in about two weeks, he says, though the specific timeline here can vary from person to person. This means you will need to take an increasingly higher dose to achieve the same effect. Higher doses mean a greater risk of side effects, like next-morning sleepiness. If you take a medication with DPH for extended periods, you might get into a vicious cycle of needing more yet feeling even sleepier throughout the day.
Here’s something you may not know: DPH is the sole active ingredient in both Benadryl and ZzzQuil. But only one is indicated for helping you fall asleep.
Although Benadryl lists “marked drowsiness” as a potential side effect, it is not indicated for sleep on its packaging. In fact, Johnson & Johnson, the makers of Benadryl, declined to comment on this subject as it discusses an off-label use.
ZzzQuil products, on the other hand, have the exact same active ingredient. (Except for one that only has the active ingredient melatonin.) Therefore, these ZzzQuil products essentially work in the same way as Benadryl, but they’re marketed specifically to help you get sleep—in the short-term, that is. ZzzQuil is indicated for “the relief of occasional sleeplessness,” and the warning label advises consumers to stop use and consult a doctor if they’re still having trouble sleeping after two weeks. When reached for comment, Procter & Gamble, the makers of ZzzQuil, emphasized these instructions. Benadryl doesn’t contain any such warning, even though experts agree that it’s not good to take it over the long term.
But taking ZzzQuil to help you sleep could, theoretically, come with the same potential side effects of taking Benadryl, like next-day sleepiness. On the ZzzQuil site, the manufacturers note that there are “many factors” that could influence how well rested you feel the next morning, including the time you take ZzzQuil. They recommend you only take ZzzQuil if you know you’ll have enough time to get a full night’s rest, however much that usually is for you.
So, why is one drug marketed as an antihistamine and one marketed as a sleep aid? It really comes down to two companies deciding how they’d like to sell a product has two major effects: reducing allergy symptoms and inducing drowsiness. Benadryl is an allergy-relief brand; ZzzQuil is a sleep-aid line, so they’ve focused on marketing what is essentially the same product in different ways. “Yes, it is the same compound [DPH], but … for a person to sleep well with any product, they have to have a certain amount of trust in the product,” Dr. Pelayo says. Some people may feel more confident that a medication marketed to help them fall asleep will do so than a medication used off-label. What’s more, “some people trust certain brands more or have preferences on how things taste or are formulated,” he says.
Also, as Dr. Pelayo points out, different drugs contain additional ingredients that are listed as inactive. It’s easy to think an inactive ingredient doesn’t do anything, but that’s not true. Inactive ingredients don’t bring about the indicated effects of a medicine, according to the Food and Drug Administration (FDA). But they may affect the taste, color, ease of active ingredient delivery, and other factors of a drug. This can lead to someone having a preference of Benadryl over ZzzQuil, or vice versa, even though they essentially work the same way.
In general, using a DPH product to help you fall asleep occasionally is fine, but it shouldn’t become a habit.
As long as you don’t mind the potential next-day drowsiness, then sporadic use of the recommended daily dose of these drugs typically won’t have serious medical repercussions for a healthy adult, Dr. Rapoport says. However, if you feel the need to turn to a sleep aid every night, you should seek treatment to address the underlying cause of your insomnia.
While it’s normal to have short periods of time where you can’t sleep well (during a hugely stressful week at work, for instance), regularly having trouble falling or staying asleep is a sign that something deeper is going on. “If you need to take something more than twice a week and the problem has gone on for more than three months, then you need to see someone,” Dr. Pelayo says. (Honestly, you should ask your doctor before even taking an antihistamine every so often to help with sleep, according to the Mayo Clinic. Drugs containing DPH can exacerbate certain underlying conditions you may have, like asthma and sleep apnea.)
A primary care doctor or sleep specialist can help you identify any underlying conditions causing your urge to reach for something in your medicine cabinet, such as anxiety. “There’s a pretty good chance that if you talk to somebody who knows what they’re talking about, we can find out what’s going on,” Dr. Rapoport says. Treating that condition can in turn help relieve the insomnia.
A doctor can also help you figure out if there are habits you may not realize are disturbing your sleep, like drinking tea late in the day, and help you work on establishing good sleep hygiene, like sticking to a consistent bedtime.
If your sleeplessness has no apparent cause, then it’s called primary or idiopathic insomnia. “The good news is that it’s very treatable,” Dr. Pelayo says. He and Dr. Rapoport both recommend cognitive behavioral therapy (CBT) to help you explore the stress or anxiety that’s come to surround sleep itself as a result of the insomnia. A therapist can help you identify and change thoughts and behaviors that may be affecting your sleep. There are even therapists who specialize in CBT for insomnia. And, while you’re figuring out treatment, your doctor may prescribe you a sedating anti-anxiety drug if they think that will help in the short term, Dr. Pelayo says.
The bottom line: Reaching for an antihistamine to help you sleep may not be harmful for most people, but it also won’t be the most helpful solution. Check in with your doctor for more suitable options.