Many antihistamines can cause drowsiness. It’s not recommended to take them for sleep, as little research backs up their effectiveness. Long-term use may also lead to harmful side effects.

Some people use over-the-counter drugs to fall asleep faster. These include sleep aids and allergy drugs that contain antihistamines, such as:

While diphenhydramine and doxylamine succinate are approved by the FDATrusted Source to help with sleep, some studies do not recommend their use due to daytime side effects.

Long-term use of antihistamines may have potential side effects that can be dangerous, especially in older adults.

Antihistamines stop allergic reactions by blocking the effects of histamine in the body. Some also block histamine release in the brainTrusted Source.

The sleep-wake cycle is regulated by chemicals that are naturally produced by your body. As you get ready for sleep, histamine levels in the brain decrease. This works to induce non-rapid eye movement sleep (NREM).

Antihistamines, such as diphenhydramine and doxylamine succinate, cross the blood-brain barrierTrusted Source, mimicking this natural function. This is why you may feel sleepy when you take medications containing them.

Medications containing these ingredients

Diphenhydramine can be found in a variety of over-the-counter medications. They include:

  • Benadryl
  • Waldryl
  • Sominex
  • Tylenol PM
  • Sudafed PE Day/Night Sinus Congestion
  • Unisom Sleep Gels

Doxylamine succinate can be found in a number of over-the-counter medications, including:

  • Unisom Sleep Tabs
  • Wal-Som
  • Vicks NyQuil Cold & Flu Nighttime Relief

In addition to blocking histamine, diphenhydramine and doxylamine succinate have anticholinergic propertiesTrusted Source. Anticholinergic drugs inhibit the action of acetylcholine in the central and peripheral nervous system.

Memory issues

Acetylcholine is a neurotransmitter that plays a pivotal role in several brain functions, including short-term memory and thinking. Anticholinergic medications can produce cognitive impairment that persists even after you stop taking them.

A 2021 review of 14 studies found that taking anticholinergic medications increased the risk for dementia and Alzheimer’s disease, and that higher exposure to these medications increased this risk.

Pregnancy and nursing

If you’re pregnant or nursing, it makes sense to be extra careful about the medications you take.

While the FDA has found Benadryl safe to take for allergies during pregnancy, they haven’t made a recommendation concerning the nightly use of a sleep aid in this population.

For this reason, it may make sense to use first-generation antihistamines sparingly or not at all, especially as sleep aids, if you’re pregnant or nursing.

Potential side effectsTrusted Source of antihistamines include:

At high doses, side effects may includeTrusted Source decreased coordination, euphoria, and delirium.

Rather than antihistamines or a sleep aid, the American Academy of Sleep Medicine recommends cognitive behavioral therapy (CBT) as a first-line treatment for insomnia.

CBT focuses on sleep hygiene and strengthening the bed-sleep connection. It helps adjust circadian rhythm and reduces anxiety about insomnia.

Sleep hygiene tips

Here are a few habitsTrusted Source you can incorporate into your routine to promote better sleep:

  • Try to go to bed and get up at the same time every day, including on weekends.
  • Avoid alcohol, caffeine, and large meals during evening hours.
  • Avoid using electronic devices at least half an hour before bed. Instead, to occupy your mind, try reading or journaling.
  • Keep the bedroom at a cool temperature. You can do this by running a fan, opening a window, or sleeping on cooling sheets.
  • Shut out light from outside with blackout curtains. Cover any sources of light in your room.
  • Keep noise to a minimum. You can also use a white noise machine to block out unwanted sound.
  • Ensure you get regular exercise during the day.
  • Eat a balanced diet.

Even though many sleep aids are available over-the-counter, it is still recommended that you talk with your doctor before starting on any new medications.

There are also natural sleep aids you may wish to consider, such as melatonin or L-theanine (γ-glutamylethylamide).

Melatonin is a hormone that’s produced naturally by the body. It doesn’t make you sleepy, but it does help your body get ready for sleep by regulatingTrusted Source your natural circadian rhythm.

Since it hasn’t been studied extensivelyTrusted Source during pregnancy, make sure you check with your doctor before using if you’re pregnant or nursing.

Long-term use of melatonin is not recommendedTrusted Source.

L-theanine is an amino acid found in tea leaves.

Even though it doesn’t make you drowsy, one studyTrusted Source found that it supports high-quality sleep by:

If you have chronic insomnia, talk with a medical professional. They may recommend prescribed sleep aids or antidepressants with a sedating effect.

Many prescription sleep aids pose some potential risks and may not be appropriate for everyone. Pregnant people and people with certain health conditions, such as liver or kidney disease, shouldn’t take certain prescription sleep aids.

Some sleep aids may also have unwanted side effects, such as dizziness. You may also become dependent on them to fall asleep.

People sometimes use antihistamines, such as diphenhydramine and doxylamine succinate, to combat insomnia.

These over-the-counter medications are OK for occasional use in most people. However, they may increase the risk for dementia and Alzheimer’s disease if taken long term.

Instead, you may want to try alternative sleep aids like melatonin, good sleep hygiene, and cognitive behavioral therapy.

If chronic insomnia is a problem, talk with a healthcare professional. They may also prescribe medications that can help.