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Zyrtec Vs Benadryl: Understanding Their Function  

An allergy is an immune reaction to a substance called an allergen. The immune system recognizes these allergens as “foreign” and “harmful” and mounts an attack against them. Examples of some common allergies include pollen, dust, pet dander, foods, and drugs. 

An allergic reaction occurs when the immune system launches a response against the allergens. This response triggers the release of chemicals like histamines, which cause allergy symptoms such as sneezing, runny/itchy nose, and red/watery eyes, among others.

These reactions are part of the body's self-defense mechanism. However, when someone is allergic to pollen, dust, or pet dander, the allergic response is typically a "false alarm" since these allergens are generally harmless. 

Antihistamines are medicines that treat allergy symptoms by blocking the effects of histamine. These drugs can treat symptoms of allergic rhinitis (hay fever or seasonal allergies). They can also be used to treat acute allergic reactions to drugs (skin rash, hives, itching). In addition, antihistamines can be used to treat acute food allergic reactions and other allergies.

Benadryl and Zyrtec are two common OTC (over-the-counter) antihistamines or H1 receptor blockers. The U.S. Food and Drug Administration (FDA) approved both medications for temporary relief from allergy symptoms. Please continue reading to learn more about the key differences between these two antihistamines. 

What is Zyrtec?

Zyrtec is a brand name product for the generic drug cetirizine hydrochloride. It is a second-generation antihistamine and is available OTC. Compare Zyrtec and Claritin.

What is Benadryl?

Benadryl is a brand name product for the generic drug diphenhydramine hydrochloride. It is a first-generation antihistamine and is available over the counter. 

Key Differences Between Zyrtec and Benadryl

• Drug Class: Zyrtec is a second-generation antihistamine. Benadryl is a first generation antihistamine.

• Approved Age Range: Zyrtec is approved for use in adults and children 2 years of age and older. Benadryl is approved for use in adults and children 6 years of age and older.

• Dosage Forms: Cetirizine (Zyrtec) comes as tablets, chewable tablets, dissolving tablets, syrup, and liquid gels. Diphenhydramine (Benadryl) comes in capsules, chewable tablets, gel caps, liquid solutions, sprays, creams, and gels.

• Standard Dosage in Adults: Zyrtec 10 milligrams (mg) by mouth once a day. Benadryl 25 mg to 50 mg by mouth every 4 to 6 hours.

• Sedative Effects: Second generation antihistamines like Zyrtec cause less sedation (drowsiness) compared to first generation antihistamines like Benadryl.

• Onset of Action: The effects of Zyrtec typically begin in 20 to 60 minutes. The effects of Benadryl typically begin in 15 to 30 minutes.

• Duration of Action: The effects of cetirizine last for about 24 hours. The effects of Benadryl usually last for 4 to 6 hours.

• Side Effects: Zyrtec is less likely to cause sleepiness and drying side effects (anticholinergic effects) like dry mouth, dry eyes, dry throat, and constipation compared to Benadryl.

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Conditions Treated By Zyrtec and Benadryl  

Allergy Symptoms  

Both Benadryl and Zyrtec are used to treat symptoms of allergic rhinitis (seasonal allergies or hay fever), such as stuffy nose or nasal congestion, runny nose, sneezing, itching in the nose, swelling of the nasal passages, itchy eyes, and watery eyes. 

Combination products are available for both Benadryl and Zyrtec, such as

• Zyrtec-D, which contains an antihistamine (cetirizine) and a decongestant pseudoephedrine

• Benadryl Allergy Plus Congestion, which contains an antihistamine (diphenhydramine) and a nasal decongestant (phenylephrine)

Compare Decongestants Vs. Antihistamines.

Specific Conditions Targeted

FDA-approved uses of Zyrtec include:

• Allergic rhinitis (seasonal allergies to pollen, grass, ragweed, etc., that are worse during allergy season).

• Perennial allergies (year-round allergies to pet dander, mold, dust mites, etc). 

• Chronic urticaria (hives, itching).

FDA-approved uses of Benadryl include:

• Allergic rhinitis.

• Cough, sore throat, and throat irritation.

• An allergic reaction in the skin (topical diphenhydramine can be used to treat pain, itching, swelling, rash, and other allergic symptoms caused by insect bites or sunburn).

• Motion sickness.

• Insomnia (difficulty falling asleep or staying asleep).

• Abnormal movements in people with early Parkinson’s disease.

Comparing Effectiveness: Zyrtec vs Benadryl  

Efficacy in Symptom Relief from Allergy Symptoms

There aren’t many head-to-head clinical trials or studies directly comparing Benadryl (diphenhydramine) and Zyrtec (cetirizine) in treating allergies. One study found that Zyrtec and Benadryl were equally effective in treating food allergies and took the same amount of time to start working, but the effects of Zyrtec lasted longer.

Speed of Relief to Treat Allergies

Benadryl starts working in 15 to 30 minutes and may provide slightly faster allergy relief than Zyrtec, which starts working in 20 to 60 minutes.

Duration of Action 

Zyrtec has a longer duration of action than Benadryl. The effects of Benadryl last for 4 to 6 hours, and you need to take it several times a day. The effects of Zyrtec last for up to 24 hours, and you only need once-daily dosing.

Evaluating Side Effects of Zyrtec And Benadryl  

Common Side Effects 

Common side effects of Benadryl (diphenhydramine) include drowsiness, dizziness, dry mouth, dry throat, constipation, nausea, vomiting, loss of appetite, chest congestion, muscle weakness, headache, nervousness, and abnormal excitement (in children).

Common side effects of Zyrtec (cetirizine) include drowsiness, dry mouth, tiredness, abdominal pain, nausea, vomiting, and diarrhea.

Serious Side Effects

Seek immediate medical care if you develop vision problems, pain with urination, or difficulty urinating after taking Benadryl. Use caution when giving Benadryl to children, as serious side effects, such as seizures, can occur if too high of a dose is administered.

Call your doctor right away or seek emergency medical attention if you develop difficulty breathing or swallowing after taking Zyrtec.

Contraindications

Benadryl may not be safe for older adults above age 65 years and people with medical conditions such as lung problems (asthma, chronic bronchitis, emphysema), glaucoma, stomach ulcers, urinary symptoms due to an enlarged prostate gland, high blood pressure, heart disease, hyperthyroidism (overactive thyroid gland), and seizures.

Zyrtec may not be safe for people with liver disease or kidney disease.

Pregnant women and those who are breast-feeding should check with their doctor before taking OTC Benadryl or OTC Zyrtec.

Safety Considerations and Drug Interactions  

Interaction With Other Medications  

Interactions between antihistamines and other medications can increase the risk of serious adverse effects. Talk to your doctor or pharmacist before taking over-the-counter antihistamines if you are on other drugs that can also have sedating effects. Possible interactions include:

• Over-the-counter cough suppressants

• Opioid pain relievers

• Muscle relaxants

• Anti-anxiety medications

• Antidepressants called monoamine oxidase inhibitors

• Psychiatric medications 

• Antiseizure drugs

• Certain medications used to treat lung conditions

• OTC cold and allergy remedies 

• Sedatives, tranquilizers, and sleep medicines

Impact on Daily Activities  

Benadryl and Zyrtec can cause drowsiness, dizziness, fatigue, blurred vision, reduced alertness, and decreased concentration. As mentioned, Zyrtec causes less drowsiness, but it can still make you feel sleepy. Be careful while driving, climbing ladders, or operating heavy machinery until you know how these medicines affect you.

Specific Warnings and Precautions

• Do not use antihistamines to make a child drowsy or sleepy.

• Do not combine multiple over-the-counter products containing the same active ingredient, as this can lead to an overdose. 

• Avoid alcohol while on medication such as Benadryl and Zyrtec. Alcohol can make side effects like drowsiness, dizziness, and impaired coordination worse.

Making an Informed Choice: Zyrtec or Benadryl  

Which Is Better To Take: Zyrtec or Benadryl?

Both Benadryl and Zyrtec can treat allergies and you can take either medicine. However, in general, newer, nonsedating, second generation antihistamines like Zyrtec are preferred over older, sedating, first generation antihistamines like Benadryl because they are safer, more effective, and cause fewer side effects. 

However, this does not mean that you should never use a first-generation antihistamine such as Benadryl. It may be the better choice for certain patients and in certain situations. For example, if you have insomnia and the drowsiness side effect of Benadryl is desirable as a sleep aid. Or if you have severe itching from atopic dermatitis and the sedative effect of Benadryl can help you sleep at night.

Also, the efficacy and tolerability of medications can vary from person to person. You can try OTC Zyrtec and OTC Benadryl and see which one works better for you with fewer side effects. Your healthcare provider and pharmacist can help you pick the right product for your symptoms as well. 

Recommendations for Specific Situations and Populations

Check with your child’s doctor before giving Zyrtec or Benadryl to a child. Do not give antihistamines formulated for adults to children. Read the package label carefully and do not exceed the maximum dosage advised for a specific age group. 

Older adults (age 65 years and older) should talk to their healthcare provider before taking Benadryl, as there may be other safer antihistamines available. Zyrtec may be safer for this age group.

Other factors that can influence the choice between Benadryl and Zyrtec include:

• Efficacy of Benadryl vs Zyrtec: One may work better for you than the other.

• Side effects: You may tolerate one medicine better than the other.

• Convenience: Zyrtec offers the convenience of daily dosing versus Benadryl which needs to be taken every 4 to 6 hours.

• Coexisting medical conditions: The presence of other conditions and symptoms can influence the choice of antihistamine (Benadryl may be preferred if you have motion sickness or insomnia, for example).

• Insurance coverage: Health insurance plans do not usually cover over-the-counter antihistamines like Benadryl and Zyrtec. However, these drugs may be covered if they are prescribed by your healthcare provider.

• Cost: 30 tablets of 10 mg cetirizine (generic Zyrtec) cost around $12 while 24 tablets of 25 mg diphenhydramine (generic Benadryl) cost around $9. A BuzzRx free discount coupon can help you save money on your antihistamine prescriptions.

Conclusion and Expert Recommendations: Why Is Zyrtec Better?

The American Academy of Allergy, Asthma & Immunology recommends newer second-generation antihistamines like Zyrtec over older first-generation antihistamines like Benadryl because the newer antihistamines:

• Are longer-acting

• Cause fewer side effects, including less drowsiness

• Are less likely to have clinically significant drug interactions

• Have a better safety profile, including a lower risk of overdose

What Is The Most Effective Antihistamine?

The most effective antihistamine depends on your symptoms, health conditions, and other factors. Some of the most effective antihistamines include: 

First-generation antihistamines

• Diphenhydramine (Benadryl)

• Hydroxyzine (Atarax, Vistaril)

• Chlorpheniramine (Chlor-Trimeton) 

• Cyproheptadine (Periactin)

Second-generation antihistamines

• Cetirizine (Zyrtec)

• Levocetirizine (Xyzal)

• Loratadine (Claritin)

• Desloratadine (Clarinex)

Third-generation antihistamines

• Fexofenadine (Allegra)

Second- and third-generation antihistamines are generally preferred over first-generation antihistamines because they're less likely to cause drowsiness and impaired cognitive function. 

Before taking an antihistamine, you should check the leaflet that comes with the medication to see if it's safe for you. You can also consult with a healthcare provider or pharmacist for medical advice. 

Why Is Benadryl Not Recommended Anymore?

Benadryl is not recommended anymore because there are newer antihistamines available that are equally effective and safer. Newer antihistamines do not cross the blood-brain barrier and, therefore, cause fewer central nervous system side effects like sleepiness and impaired cognition. However, Benadryl may still be useful in certain situations.