Benadryl vs Zyrtec

Listen to the article instead of reading through it.


For patients with allergies, certain drugs can help alleviate symptoms by blocking the effects of histamines in the body. Benadryl and Zyrtec are two such medications that are commonly used to manage allergic reactions. Each drug operates differently but both ultimately work towards relieving allergy-induced discomfort. Benadryl (Diphenhydramine) is a first-generation antihistamine, which means it tends to cross the blood-brain barrier more often and cause side effects like drowsiness. On the other hand, Zyrtec (Cetirizine) is a second-generation antihistamine that specifically targets peripheral histamine receptors, reducing systemic side effects such as sedation. Both offer relief from symptoms like runny nose, sneezing, itchy or watery eyes but they differ significantly in their duration of action and propensity for causing sleepiness.

What is Benadryl?

Diphenhydramine (the generic name for Benadryl) is a first-generation antihistamine. It was developed in the mid-20th century and has been an over-the-counter medication staple ever since. Benadryl works by blocking histamines, substances that the body produces during allergic reactions or inflammation to get rid of allergens, effectively reducing allergy symptoms such as sneezing, itching, watery eyes, and hives.

On the other hand, Cetirizine (the generic name for Zyrtec) is a second-generation antihistamine which came into use in 1987. Like Benadryl, it also blocks histamine but with one significant difference: it does not cross the blood-brain barrier as readily as diphenhydramine does. This results in less drowsiness and sedation compared to older first-gen antihistamines like Benadryl - a major development upon these earlier drugs.

Both are prescribed for treating symptoms caused by allergies; however Zyrtec's selectivity towards peripheral vs central nervous system histamine receptors leads to fewer side effects than those associated with medications affecting both systems more equally.

What conditions is Benadryl approved to treat?

Benadryl and Zyrtec are approved for the treatment of various allergy-related conditions:

  • Allergy symptoms such as runny nose, sneezing, itchy or watery eyes, and itching of the nose or throat
  • Chronic urticaria (hives) Note that while both drugs treat similar conditions, they have different active ingredients - Benadryl contains diphenhydramine while Zyrtec contains cetirizine. These differences may influence their side effect profiles and how they interact with other medications.

How does Benadryl help with these illnesses?

Benadryl helps to manage allergy symptoms by blocking the action of histamine, a compound that is released in the body during an allergic reaction. It does this by binding to and inhibiting the H1 receptor sites on cells throughout your body, preventing histamine from causing its typical effects like itching, sneezing, runny nose or hives. Histamine plays an important role in immune responses, regulating gut function and acting as a neurotransmitter for the brain, spinal cord and uterus among other things.

However, unlike newer antihistamines like Zyrtec (cetirizine), Benadryl can cross into your brain from the blood and cause drowsiness. This crossing of the blood-brain barrier also contributes to some of its side effects such as dry mouth or blurred vision. In contrast, Zyrtec doesn't readily enter your brain from your bloodstream leading to less sedation than older generation antihistamines like Benadryl while still providing effective relief against allergies.

What is Zyrtec?

Zyrtec, which is a brand name for cetirizine, is an antihistamine that blocks the action of histamine in your body to reduce symptoms of allergies. It was first approved by the FDA in 1995. Unlike older antihistamines like Benadryl (diphenhydramine), Zyrtec does not cross the blood-brain barrier as readily, meaning it doesn't have as significant an effect on the central nervous system and therefore causes less sedation. This makes Zyrtec a better choice for daytime use or for those who need to manage allergy symptoms without feeling drowsy. While both medications can effectively treat allergic symptoms such as runny nose, sneezing, itchy or watery eyes and itching of the nose or throat; due to its minimal sedative effects and longer duration of action (up to 24 hours compared with Benadryl’s six hour maximum), many people find Zyrtec more suitable for their needs.

What conditions is Zyrtec approved to treat?

Zyrtec, a second-generation antihistamine, is cleared by the FDA for handling several conditions:

  • Seasonal allergic rhinitis (hay fever)
  • Perennial allergic rhinitis (year-round allergies)
  • Chronic idiopathic urticaria (chronic hives without a known cause)

How does Zyrtec help with these illnesses?

Histamine is a chemical that your body releases during an allergic reaction. It triggers symptoms like sneezing, itching, and runny nose. Zyrtec (cetirizine), much like Benadryl (diphenhydramine), works by blocking the effects of histamine in the body, thus reducing these symptoms. However, Zyrtec has a major advantage: it's a second-generation antihistamine. This means it's less likely to cross the blood-brain barrier and cause drowsiness — a common side effect associated with first-generation antihistamines like Benadryl. Moreover, Zyrtec is typically longer acting compared to Benadryl which has to be taken every four to six hours. Hence for individuals needing long-term management of their allergy symptoms or those who want to avoid feeling sleepy after taking their medication, Zyrtec could be a more suitable choice.

How effective are both Benadryl and Zyrtec?

Both diphenhydramine (Benadryl) and cetirizine (Zyrtec) are antihistamines with established histories of successfully treating allergy symptoms. Diphenhydramine was approved by the FDA in 1946, while cetirizine was approved much later in 1995. Both medications function by blocking histamine receptors, but they have different characteristics due to their classifications as first- and second-generation antihistamines.

In a double-blind clinical trial conducted in 2000 comparing the two drugs, both were found effective at controlling allergy symptoms such as sneezing, runny nose, itchy or watery eyes. Although efficacy between these two was similar for most metrics studied to measure relief from hay fever symptoms, Zyrtec had an edge over Benadryl when it came to improving nasal obstruction.

A review of studies on diphenhydramine showed that this drug starts working within one hour after administration and reaches its peak effect after one to three hours. However, because of its sedative properties - which can be severe - and shorter duration of action requiring multiple doses a day; it's generally not considered the first choice for treating allergies especially when non-sedating options like Zyrtec are available.

On the other hand, a meta-analysis from 2018 highlighted that cetirizine is an effective treatment for allergic rhinitis with minimal side effects compared to placebo or other second-generation antihistamines. It typically takes effect within an hour and has a longer duration of action allowing once-daily dosing making it more convenient than Benadryl. Furthermore, unlike diphenhydramine which can cause significant drowsiness; cetirizine is classified as minimally sedating.

abstract image of a researcher studying a bottle of drug.

At what dose is Benadryl typically prescribed?

Oral dosages of Benadryl range from 25-50 mg every 4-6 hours for adults and children over the age of 12. For children aged 6 to under 12 years, the dosage ranges from 12.5–25 mg every four to six hours. However, studies have indicated that a single dose is often enough for relief from symptoms like congestion or hives. On the other hand, Zyrtec can be taken at a dosage of one tablet (10mg) once daily by adults and children over six years old. Children between two to five years old may start with half a tablet (5mg). In either case, do not exceed the recommended dose without consulting your doctor.

At what dose is Zyrtec typically prescribed?

Zyrtec treatment generally begins with a dosage of 10 mg/day for adults and children aged 6 years or older. For children between the ages of 2-5, it is typically started at a lower dose; usually around 2.5mg (half a tablet) once daily in the morning or evening. The dose can be increased to up to two doses per day (spaced out by about 12 hours), if there is no response after an initial few days on Zyrtec therapy. A maximum dose of 10mg per day should not be exceeded unless directed by your healthcare provider as this may increase the risk of side effects such as drowsiness.

What are the most common side effects for Benadryl?

While both Benadryl and Zyrtec are used to treat allergy symptoms, they come with different side effects. Common side effects of Benadryl may include:

  • Drowsiness/sleepiness
  • Dry mouth
  • Dizziness
  • Nausea
  • Vomiting
  • Loss of coordination or balance
  • Constipation

Zyrtec, on the other hand, can cause:

  • Drowsiness/sleepiness
  • Fatigue (general weakness)
  • Dry mouth
  • Nausea
    -Stomach pain

However, these medicines could affect individuals differently. It's important to consult your healthcare provider to decide which medication is right for you based on your medical history and current medications.

abstract image of a patient experiencing side effect

Are there any potential serious side effects for Benadryl?

While both Benadryl and Zyrtec are antihistamines used to treat allergies, they can have different side effects. It's important to be aware of these potential issues:

  • Severe allergic reaction: Symptoms include developing hives, having difficulty breathing, experiencing swelling in your face or throat.
  • Dry mouth or throat, blurred vision or trouble urinating
  • Drowsiness: This is a common side effect with Benadryl but less so with Zyrtec.
  • Fast or irregular heartbeat; feeling like you might pass out.
  • Mental/mood changes such as confusion, hallucinations
  • Difficulty urinating.

Severe nervous system reaction - restlessness, insomnia (particularly in children), and even convulsions may occur in rare cases. In some instances where high dosage is taken for an extended period of time – dependence on the drug may develop.

If any of these symptoms appear after taking either medication seek immediate medical assistance

What are the most common side effects for Zyrtec?

Zyrtec, compared to Benadryl, may share some similar side effects but also has its unique ones:

  • Mild drowsiness or fatigue
  • Dry mouth or sore throat
  • Nausea, stomach pain
  • Headache and occasional dizziness
  • Constipation or diarrhea Additionally, it's important to note that Zyrtec is less likely than Benadryl to cause sedation - a significant advantage for those needing relief from allergy symptoms during the day. Always remember that individual reactions can vary widely; monitor your body's response closely when starting any new medication.

Are there any potential serious side effects for Zyrtec?

While Zyrtec is generally considered safe, in some cases, it may cause serious side effects. These can include:

  • Signs of a severe allergic reaction: including hives; difficulty breathing; swelling of your face, lips, tongue, or throat
  • Confusion or unusual changes in behavior: feeling restless or nervous
  • Problems with vision such as blurred vision
  • Rapid heartbeat and tremors
  • Urination problems: little to no urinating If you experience any of these side effects while taking Zyrtec, it is crucial that you immediately seek medical attention.

Contraindications for Benadryl and Zyrtec?

Benadryl and Zyrtec, like many antihistamines, may cause drowsiness or other side effects such as dry mouth or stomach upset. If you notice your symptoms worsening or if there's an increase in sleepiness that affects your daily functioning, please contact a healthcare professional immediately.

Neither Benadryl nor Zyrtec should be taken if you are using, or have recently been taking monoamine oxidase (MAO) inhibitors. It is essential to inform your physician about all the medications you are currently on; MAOIs will require a period of approximately 2 weeks to eliminate from your system to prevent harmful interactions with Benadryl and Zyrtec.

How much do Benadryl and Zyrtec cost?

For the brand name versions of these drugs:

  • The price of 24 tablets of Zyrtec (10 mg) averages around $18, which works out to approximately $0.75/day.
  • The price for 100 capsules of Benadryl (25 mg) is about $12, working out to roughly $0.12/day.

Thus, if you are taking one dose per day as recommended for both medications, Benadryl is less expensive on a per-day treatment basis. However, cost should not be your primary consideration in determining which drug is right for you.

As for generic versions - cetirizine (Zyrtec) and diphenhydramine (Benadryl), costs are significantly lower:

  • Cetirizine can be purchased in packs ranging from 14 to hundreds of tablets with approximate costs starting from as low as $0.05/day up to about $0.30/day depending on the pack size bought.

  • Diphenhydramine is available in larger quantities with pack sizes going up to several hundred capsules and similar pricing structure at approximately $0.02–$0.10 per day depending on quantity bought upfront.

In both cases, opting for generics generally offers remarkable savings compared to their brand-name counterparts.

Popularity of Benadryl and Zyrtec

Diphenhydramine, under brand names such as Benadryl, is one of the most commonly used first-generation antihistamines and has been a go-to for seasonal allergies, insect bites, and occasional insomnia due to its sedative effects. About 5 million Americans used diphenhydramine in 2020. It accounts for approximately 10% of over-the-counter antihistamine sales in the US.

On the other hand, Cetirizine or Zyrtec is a second-generation antihistamine that offers relief from allergy symptoms with less risk of drowsiness than first-generation options like diphenhydramine. In 2020, it was estimated that cetirizine was chosen by about 6 million people in America to combat their allergies. This makes cetirizine responsible for just under 15% of all over-the-counter sales among non-sedating antihistamines. The use of Zyrtec has seen an increase since it became available without prescription in 2008.


Both Benadryl (diphenhydramine) and Zyrtec (cetirizine) have long-standing records of usage in patients with allergies, backed by numerous clinical studies indicating that they are more effective than placebo treatments. They both work as antihistamines to reduce allergy symptoms such as runny nose, sneezing, itchy or watery eyes, hives and itching.

Due to their different pharmacological characteristics though, they tend to be used under different circumstances. Benadryl is known for its fast-acting relief but has a shorter duration of action compared to Zyrtec; thus it can be useful for acute allergic reactions. However, its main drawback is drowsiness which can affect daily activities.

Zyrtec on the other hand provides 24-hour relief from allergy symptoms without causing significant sedation making it suitable for regular use without interfering with day-to-day activities. It’s also less likely to interact with alcohol or other medications compared to Benadryl.

Both drugs are available over-the-counter which represents significant cost savings especially for people who need them regularly. The side effect profile between these two drugs varies significantly due mainly because of differences in sedative effects - while both are generally well-tolerated, Zyrtec tends not cause sleepiness unlike Benadryl.

For either medication patients should monitor how they feel after taking the drug and consult a healthcare provider if there's an increase in severity of symptoms or emergence of new ones like difficulty breathing or swelling around face/lips/tongue/throat since these could signal severe allergic reaction requiring immediate medical attention.