Hydroxyzine is a first-generation antihistamine, commonly prescribed to reduce anxiety and tension, relieve itching from allergic reactions, and provide sedation before medical procedures. It is available in various forms, including oral tablets, capsules, and syrup.
How Hydroxyzine Works and Its Immediate Effects
Hydroxyzine primarily functions as a potent inverse agonist of the histamine H1 receptor. This action blocks the effects of histamine, a natural chemical in the body that contributes to allergic reactions like itching and hives. Beyond its antihistamine properties, hydroxyzine also influences the central nervous system, producing sedative and anxiolytic (anxiety-reducing) effects. Its calming action is thought to occur by suppressing activity in certain subcortical areas of the brain.
The effects of hydroxyzine are typically felt relatively quickly after administration. Oral doses usually begin to work within 15 to 30 minutes, with the medication reaching its peak concentration in the body around two hours later. Its noticeable therapeutic effects, such as drowsiness or itch relief, generally last for about 4 to 6 hours. This duration of immediate therapeutic action means that hydroxyzine may be prescribed multiple times a day to maintain its effects.
How Long Hydroxyzine Stays in Your System
The duration of hydroxyzine’s therapeutic effects differs from how long the drug remains detectable in the body. The time it takes for the body to eliminate half of a drug is known as its half-life. For hydroxyzine, the average half-life in adults ranges from 14 to 25 hours, commonly cited as approximately 20 hours. Complete elimination of a medication from the body typically requires about five half-lives.
Hydroxyzine can stay in the system for approximately 70 to 125 hours, or roughly 3 to 5 days, after the last dose. The body processes hydroxyzine primarily in the liver through enzymes like CYP3A4 and CYP3A5. Its main active metabolite, cetirizine, which is also an antihistamine, is formed during this process and is largely excreted unchanged in the urine. However, the noticeable effects of hydroxyzine typically subside much earlier than its complete elimination from the system.
Factors Influencing Hydroxyzine’s Duration
Several individual factors can influence how long hydroxyzine’s effects last and how long it remains in the body. The prescribed dosage plays a role, as higher doses generally lead to more pronounced and potentially longer-lasting effects. Individual metabolism rates also vary significantly among people, affecting how quickly the body breaks down and eliminates the drug.
Age is another important factor, with older adults often metabolizing drugs more slowly, leading to a prolonged half-life of around 29 hours. Children tend to metabolize hydroxyzine more quickly, with an average half-life of about 7 hours. The function of the liver and kidneys is crucial for drug elimination. Impaired liver or kidney function can significantly extend the time hydroxyzine stays in the system, as these organs are responsible for its metabolism and excretion, potentially increasing the risk of side effects. Other medications can also interact with hydroxyzine, potentially altering its metabolism or increasing the risk of side effects like excessive drowsiness or heart rhythm issues.