How long does hydroxyzine take to work? A quick guide

In this article:

• How fast does hydroxyzine work?
• What does "working" feel like?
• Factors that influence onset
• How long does the effect last?
• What to do if it isn't working fast enough?
• When to talk to your doctor

In this article

• How fast does hydroxyzine work?
• What does "working" feel like?
• Factors that influence onset
• How long does the effect last?
• What to do if it isn't working fast enough?
• When to talk to your doctor

Hydroxyzine is a first-generation prescription antihistamine available in two formulations: hydroxyzine pamoate (brand name: Vistaril) and hydroxyzine hydrochloride (hydroxyzine HCl). Both formulations are more potent than over-the-counter options and are FDA approved to reduce anxiety and tension, to treat allergic skin reactions, to relieve nausea, and before and after procedures utilizing anesthesia to minimize potential side effects.

Hydroxyzine works quickly, usually taking effect within 15 to 30 minutes of taking it. However, there are some things that can speed up or slow down this drug’s absorption in your body. If you’ve been prescribed hydroxyzine, here’s what to expect.

How fast does hydroxyzine work?

Most people begin noticing calming effects or sedation about 15 to 30 minutes after taking hydroxyzine, according to Joy Alonzo, Pharm.D., Associate Professor of Pharmaceutical Sciences at Texas A&M Health. Even if it takes a bit longer than that, the drug still works quickly, reaching its peak concentration in your body after about 2 hours.

The timeline stays the same regardless of your reason for taking hydroxyzine, per Archana Jhawar, Pharm.D., Clinical Assistant Professor of Pharmacy Practice at the University of Illinois Chicago (UIC), Retzky College of Pharmacy. That means it should start working quickly, whether you’re taking it for anxiety, sedation, nausea, or itching due to an allergic skin reaction. 

While many healthcare providers prescribe hydroxyzine as needed for anxiety, it can also be used to reduce symptoms in people with generalized anxiety disorder (GAD), says Dr. Jhawar. Studies have shown that it effectively relieves anxiety compared to a placebo when taken regularly, with symptoms improving as early as one week after starting the medication. However, even though it’s not a controlled substance, relatively short-term use is still recommended; Dr. Alonzo says the FDA hasn’t established the effectiveness of hydroxyzine for anxiety when used for more than 4 months.  

What does “working” feel like?

The biggest sign that hydroxyzine is working is a feeling of calmness, and in many cases, drowsiness or fatigue. If you’re taking hydroxyzine for anxiety, you may also start to feel less stressed or tense. 

Because it’s an antihistamine, hydroxyzine crosses the blood-brain barrier and blocks histamine receptors, says Dr. Alonzo. These receptors can cause both allergy symptoms and nausea or vomiting, so blocking them with a drug like hydroxyzine can treat those symptoms. 

However, there are some other potential side effects of hydroxyzine that you may notice while taking it, including dry mouth, dizziness, headache, and confusion, especially in older adults. Dr. Jhawar says it can increase the risk of falls or delirium, including disorientation and hallucinations, particularly in people with dementia.

Factors that influence how fast you feel it

Most people notice the effects of hydroxyzine about 15 to 30 minutes after taking it, but some factors can change this timeline, slowing down the drug’s absorption and making it take longer to start working.

Your metabolism

Your body relies on enzymes to break down medications. This determines how quickly a drug begins working as well as how quickly it’s cleared from your system. Variations in the speed of that metabolism is high variable from person-to-person, such that a medication like hydroxyzine may not work as well for you because it might break down too quickly; if your metabolism is slow, the medication may accumulate and cause more noticeable side effects.

Your age

Older adults often experience the effects of sedating medications differently because of age-related changes in metabolism, kidney and liver function, and increased brain sensitivity to these drugs, says Dr. Alonzo. While hydroxyzine may not necessarily take longer to work in older adults, its effects may last longer and feel stronger. 

Gut motility issues

People with gut motility issues or conditions like gastroparesis often absorb hydroxyzine unpredictably because delayed gastric emptying changes when the drug actually hits the small intestine for absorption. “I’ve had patients report wildly inconsistent sedation timing, and the culprit was their underlying GI condition, not the drug itself,” explains Bharat Pothuri, MD, gastroenterologist and founder of GastroDoxs in Houston.

Liver function problems 

Hydroxyzine is heavily metabolized in the liver, per Dr. Pothuri, so impaired liver function can affect the drug’s timeline of absorption. People with liver disease or even fatty liver may have significantly prolonged effects because their liver needs more time to metabolize the drug, he explains.  

How long does the effect last?

You may feel the effects of hydroxyzine for up to 8 hours, says Jonathan Jennings, MD, internist with Medical Offices of Manhattan, though this can vary based on your age. Sometimes the effects only last 4 to 6 hours, says Dr. Alonzo, which is why it’s often taken multiple times per day. 

However, hydroxyzine stays in your system for longer than that: Per Dr. Jhawar, it has a half-life of around 20 hours. That means 50% of the dose you take will still be in your system at that time, and won’t be fully cleared until somewhere between 60 and 100 hours after your dose.

This can leave some people susceptible to a hangover-like effect after hydroxyzine wears off. Because it’s a sedating medication that slows down certain nervous system functions, Dr. Alonzo says some people might experience grogginess, slowed thinking, or “brain fog,” or fatigue the morning after taking this medication. 

Not everyone feels this way, though, and there are ways to reduce the hangover effect. According to Dr. Jennings, taking the lowest effective dose, staying well hydrated, giving yourself plenty of time to rest after dosing, and avoiding combining hydroxyzine with other sedating medications and drugs like alcohol can help prevent these symptoms.   

In addition to these suggestions, older adults, who may be more prone to confusion and extreme sedative effects, may also want to consider taking hydroxyzine earlier in the evening instead of right at bedtime and adjusting their dosing frequency, says Dr. Alonzo.

What to do if it isn’t working fast enough

Hydroxyzine doesn’t work for everyone, so if it isn’t helping much, it’s important to contact your healthcare provider. Dr. Alonzo says you may be able to slowly increase your dose or adjust the timing or frequency to see if there’s improvement. It may also be helpful to ask your provider to check for drug interactions or other reasons why you’re not getting relief, she says, and discuss non-medication strategies that can be paired with hydroxyzine, like improving your sleep hygiene or going to therapy.

Finally, you may need to switch to another medication, especially if you have long-term symptoms. For anxiety, for example, hydroxyzine is more commonly used short-term; if you’re continuing to have symptoms, your provider may recommend cognitive behavioral therapy (CBT) or antidepressants such as SSRIs (selective serotonin reuptake inhibitors), SNRIs (serotonin and norepinephrine reuptake inhibitors), or benzodiazepines instead of an increase in your hydroxyzine dose, Dr. Alonzo explains.

When to talk to your healthcare provider

Hydroxyzine is considered a safe and well-tolerated medication, says Dr. Jhawar, and most common side effects are annoying but not harmful. 

However, there are some rare side effects that could potentially be dangerous and warrant immediate medical attention. Per Dr. Jhawar, this includes:

• Signs of allergy or anaphylaxis, such as difficulty breathing, hives, and swelling of the face, lips, or tongue
• Signs of heart arrhythmia (changes in heart rhythm) or long QT syndrome, including palpitations, dizziness, and fainting 
• Priapism (an erection in men that doesn’t go away after 3 hours)

Drug interactions are also possible. The following medications can cause increased risk of adverse effects like sedation, severe sleepiness, and dangerous heart rhythm changes when combined with hydroxyzine:

• Central nervous system (CNS) depressants, including opioids, sleep medications, and benzodiazepines like Xanax (alprazolam)
• QT prolongation drugs that affect the heart rhythm, such as antidepressants like Zoloft (sertraline),
• Anticholinergic medications, including other antihistamines like over-the-counter (OTC) Benadryl (diphenhydramine).

In general, if the benefits of taking hydroxyzine are outweighed by the side effects, you should consult your healthcare provider for medical advice. You may be able to make slight adjustments to dosing that relieve those side effects, or you may need to switch to another medication.