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Drug Info

How long does hydroxyzine last?

Typically, a dose of this antihistamine works for about four to six hours
Jennifer Larson writer headshot
By | Jul. 23, 2024 Medically reviewed by Marissa Walsh, Pharm.D., BCPS-AQ ID
A pill and a clock | how long does hydroxyzine last

Key takeaways

  • Hydroxyzine is a first-generation antihistamine that’s used to treat conditions such as anxiety, insomnia, and allergic reactions.

  • Usually, hydroxyzine takes effect fairly rapidly, within a half hour.

  • A dose of this medication works for about four to six hours, but it has a long half-life, and side effects can linger for much longer.

In this article:

Hydroxyzine is a first-generation antihistamine that can be used to treat a number of different conditions, including anxiety, insomnia, and allergic reactions like hives. This medication comes in tablet, capsule, and syrup form and is sold under the brand names Vistaril and Atarax. If you’re prescribed hydroxyzine, you might be wondering how long each dose lasts, how long it takes to kick in, and what side effects to expect. You’ve come to the right place!

How long does hydroxyzine last?

A dose of hydroxyzine usually lasts for four to six hours. Hydroxyzine works by blocking the action of histamine, a chemical released by the body’s immune system in response to an allergen. However, it’s often used to treat anxiety and insomnia because it suppresses activity in certain parts of the subcortical area of the central nervous system, making you feel relaxed or sleepy.

This sedative effect may linger even longer than six hours, according to Marlene Peng, MD, an allergist with Swedish Allergy and Immunology in Seattle, Washington. In fact, because hydroxyzine has a long half-life, it can remain in your system and affect your body for up to 24 hours, especially when taken regularly. It lasts longer than over-the-counter first-generation antihistamines like Benadryl (diphenhydramine). This means that the side effects—like grogginess—may last longer, too.

How long does hydroxyzine take to work?

Hydroxyzine usually starts to take effect within 30 minutes, says Dr. Peng. You could feel symptoms of anxiety or insomnia start to improve “within hours of the first dose,” according to The National Alliance on Mental Illness (NAMI).

Most people take hydroxyzine three to four times daily, but the dose varies depending on the reason it’s prescribed. For example, an adult might take 50 mg to 100 mg four times per day for anxiety, while the dosage for allergic symptoms is 25 mg three to four times per day. For insomnia, you might take a one-time dose of 50 mg to 100 mg an hour before bed.

Hydroxyzine side effects

Like most medications, hydroxyzine has potential side effects. The most well-known is drowsiness, which is part of why it’s so effective for insomnia. Hydroxyzine crosses the blood-brain barrier and has a sedating effect, so you might start feeling sleepy and sluggish after a dose. Because of this, “you don’t want to drive a car or ride a bike on hydroxyzine,” says Dr. Peng.

Other common side effects can include:

  • Dizziness
  • Dry mouth
  • Confusion
  • Constipation
  • Fatigue
  • Headache
  • Irritability

Some of these side effects are more likely to affect older adults. “As you get older, you worry about confusion, dizziness, constipation, difficulty with your motor functions,” says Dr. Peng.

It’s also possible to experience more serious side effects from taking hydroxyzine. It’s rare, but this medication can cause a serious skin condition called acute generalized exanthematous pustulosis (AGEP), in which pustules suddenly develop on the skin. Hydroxyzine can also worsen glaucoma, benign hyperstatic hypertrophy, and COPD, says Ryan Shipe, MD, a pulmonary and critical care provider with Milford Regional Physician Group in Milford, Massachusetts.

It is possible to overdose on this medication. Seek immediate medical attention if you experience severe sedation, a racing or pounding heartbeat, agitation, vomiting, or skin reactions.

Discuss all medications and dietary supplements you are taking with your prescribing provider or pharmacist to avoid a drug interaction.

How long should you take hydroxyzine?

Short-term use of hydroxyzine is considered safe. However, long-term use is usually not recommended. “There’s no exact answer to how long it is safe for someone to take a medication like hydroxyzine,” says Savjani Prathyusha, MD, an allergist with CLS Health in Houston, Texas. Recent data has found that long-term use of first-generation antihistamines is associated with earlier-onset dementia, and so we strongly encourage patients not to use these daily long-term.”


If you have chronic allergies, “newer generation antihistamines are tolerated better over the long-term,” explains Dr. Shipe. Luckily, there are many safe and effective alternatives for each condition that hydroxyzine treats.

Hydroxyzine alternatives

Hydroxyzine is not recommended for everyone. For example, people who have a prolonged QT interval (a rare heart issue that can cause irregular heart rhythm) and people who are breastfeeding should not take hydroxyzine. For people with chronic allergies, a second-generation allergy medication “like Claritin, Allegra, Zyrtec, Xyzal, all work as well as hydroxyzine with a much better side effect profile,” says Michael McCormick, MD, an allergist with Milford Regional Physician Group.

Your healthcare provider may prescribe these alternatives instead of hydroxyzine.

Allergies or allergic reactions

For allergies or hives (urticaria), your provider might prescribe:

“In conditions such as chronic urticaria, we often use second-generation antihistamines for up to four times the standard dosing to better control hives,” says Dr. Savjani. “This is much more effective, safer long-term, and better tolerated than using first-generation antihistamines like hydroxyzine.”

Insomnia

If you have insomnia, your provider might suggest trying a non-pharmacological treatment first, such as:

  • Improving your sleep hygiene
  • Trying cognitive behavioral therapy
  • Practicing relaxation exercises


If these lifestyle changes don’t work, prescription medications such as Lunesta (eszopiclone) and Sonata (zaleplon) or over-the-counter (OTC) treatments such as Unisom (doxylamine) are available.

Anxiety

The first-line treatments for generalized anxiety disorder are antidepressants such as selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs). Many people experience success with a combination of talk therapy and one of these medications.

For anxiety attacks, benzodiazepines such as Xanax (alprazolam) take effect quickly. However, they have a greater potential for abuse or addiction, according to the DEA.

Your provider will determine the best medication based on your symptoms, medical history, and required duration of treatment.

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