The inability to fall or stay asleep can have a significant, negative impact on your mood, productivity, and overall health. Insomnia can also be stressful, making it harder to rest.

In an effort to get much-needed sleep, many people use over-the-counter drugs to fall asleep faster. These include sleep aids and allergy drugs that contain antihistamines, such as:

  • diphenhydramine
  • doxylamine succinate

Drowsiness is a common side effect of some antihistamines. However, the American Academy of Sleep Medicine doesn’t recommend using them as sleep aids, citing weak evidence for their effectiveness.

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

In this article, we’ll talk about antihistamine use for insomnia and provide recommendations for alternative treatments.

Antihistamines stop allergic reactions by blocking excess production of histamine in the immune system. Some also block histamine release in the brain.

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 barrier, mimicking this natural function. That’s why you get sleepy when you take medications containing them.

In addition to blocking histamine, diphenhydramine and doxylamine succinate have anticholinergic properties. 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 long-term 2015 study analyzed the effects of cumulative anticholinergic medication use among over 3,000 participants ages 65 and over. Study participants were followed for over 7 years.

Researchers found that taking anticholinergic medications for 3 years or more increased the risk for dementia and Alzheimer’s disease. Researchers also found an escalation of risk based upon the cumulative amount of anticholinergic medication taken over time.

Pregnancy and nursing

If you’re pregnant or nursing, it makes sense to be extra careful about the medications you take. While the Food and Drug Administration (FDA) has found Benadryl safe to take for allergies during pregnancy, they haven’t made a recommendation concerning nightly use of a sleep aid in this population.

Anticholinergic medications are FDA pregnancy category B drugs. This means that animal studies haven’t shown a risk to the fetus, but there are no adequate, well-controlled studies indicating safety.

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 effects of some antihistamines include:

  • daytime drowsiness
  • short-term memory loss
  • confusion
  • agitation
  • dry mouth
  • blurred vision
  • increased heart rate
  • difficulty urinating

Rather than antihistamines or any type of sleep aid, the American Academy of Sleep Medicine and European Sleep Research Society 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.

When choosing any over-the-counter sleep aid, check the ingredients and discuss with a medical professional whether it’s OK for you to take it short-term.

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 regulating your natural circadian rhythm. Since it hasn’t been studied extensively during pregnancy, check with your doctor before using it if you’re pregnant or nursing.

L-theanine is an amino acid found in tea leaves. Even though it doesn’t make you drowsy, a review of multiple studies found that it supports high-quality sleep by promoting relaxation and reducing anxiety.

Practicing good sleep hygiene habits can help train your body and brain to fall and stay asleep. Here are some strategies to try:

  • Avoid drinking excessive alcohol and caffeine during evening hours.
  • Don’t use electronic devices, such as computers and phones, in the 2 hours before bed. If this is challenging, use blue light screen protectors on your devices or wear eyeglasses with a blue light filter.
  • Keep the temperature in your bedroom cool by running a fan, opening a window, or sleeping on cooling sheets.
  • Shut out sources of ambient light with curtains and a closed door.
  • Keep noise to a minimum. If outdoor noise is beyond your control, use a white noise machine to block out unwanted sound.

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 risk 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 may also have unwanted side effects such as dizziness. Others may experience dependence.

Peoplpe 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.