When you have an allergic reaction, your body releases a substance called histamine. Histamine causes allergy symptoms when it binds to receptors on certain cells in your body. Antihistamines work by decreasing the effects of histamine at certain cell receptors.

Over-the-counter (OTC) antihistamines can help treat symptoms such as:

  • congestion
  • runny nose
  • sneezing
  • itching
  • nasal swelling
  • hives
  • skin rashes
  • itchy and watery eyes

Read on to learn how the different brand-name antihistamines can help treat your allergy symptoms.

First-generation OTC oral antihistamines, including diphenhydramine and chlorpheniramine, are the oldest group. They are sedating, which means they’re likely to make you drowsy after you use them. They also don’t last as long in your system, so they require more frequent dosing than the newer generations. First-generation brands include Benadryl and Chlor-Trimeton.

Benadryl

The first-generation antihistamine diphenhydramine is the main active ingredient in Benadryl. Benadryl helps relieve runny nose, sneezing, itchy or watery eyes, and nose or throat itching. These symptoms may be due to hay fever, other upper respiratory allergies, or the common cold. Benadryl can also be used to treat hives and to reduce redness and itching.

It comes in a tablet, a chewable tablet, a tablet that dissolves in your mouth, a capsule, a liquid-filled capsule, and a liquid. Benadryl also comes in topical forms, such as creams, gels, and sprays, to treat allergic skin conditions such as hives.

Other common OTC brands that include the antihistamine diphenhydramine include:

  • Banophen
  • Siladryl
  • Unisom
  • Benadryl-D Allergy Plus Sinus
  • Robitussin Severe Multi-Symptom Cough Cold + Flu Nighttime
  • Sudafed PE Day/Night Sinus Congestion

Chlor-Trimeton

Chlorpheniramine is the main active ingredient in Chlor-Trimeton. It helps relieve runny nose, sneezing, itchy or watery eyes, and nose and throat itching from hay fever. It also helps relieve other respiratory allergies.

It comes in an immediate-release tablet, an extended-release tablet, a chewable tablet, a lozenge, a capsule, and a liquid.

Other common brands with chlorpheniramine as a main active ingredient include:

  • Aller-Chlor
  • Chlorphen-12
  • Alka-Seltzer Plus Cold & Cough Liquid Gels
  • Allerest Maximum Strength
  • Comtrex

Side effects of first-generation antihistamines

Some of the more common side effects of first-generation antihistamines can include:

  • drowsiness
  • dry mouth, nose, and throat
  • headache

Some side effects that are not as common include:

  • dizziness
  • nausea
  • vomiting
  • loss of appetite
  • constipation
  • chest congestion
  • muscle weakness
  • hyperactivity, especially in children
  • nervousness

Some serious side effects can include:

  • vision problems
  • trouble urinating or pain with urinating

All of these side effects are more common in older people.

Warnings

If you have an enlarged prostate that makes it difficult for you to urinate, you should talk to your doctor before using first-generation antihistamines. These drugs can make your urination problem worse. You should also talk to your doctor before using these drugs if you have any of these health concerns:

If you take other drugs that can make you drowsy, such as sedatives or tranquilizers, talk to your doctor before using first-generation antihistamines. You should also avoid drinking alcohol with any antihistamine because it can increase the side effect of drowsiness.

The newer second-generation and third-generation OTC oral antihistamines were developed to target their action on more specific receptors. This helps decrease side effects, including drowsiness. Also, these drugs work longer in your body so you need fewer doses.

Zyrtec

Cetirizine is the main active ingredient in Zyrtec. It helps relieve runny nose, sneezing, itchy and watery eyes, and nose or throat itching from hay fever and other upper respiratory allergies. Zyrtec can also be used to help relieve redness and itching due to hives. Zyrtec comes in a tablet, a chewable tablet, a tablet that dissolves in your mouth, a liquid-filled capsule, and a syrup.

Other common OTC brands with cetirizine as the main active ingredient include:

  • Aller-Tec
  • Alleroff
  • Zyrtec-D
  • Wal Zyr-D
  • Cetiri-D

Side effects

Some common side effects of Zyrtec can include:

  • drowsiness
  • headache
  • stomach pain

Serious side effects can include trouble breathing or swallowing.

Warnings

  • Talk to your doctor if you use the bronchodilator theophylline. Zyrtec can interact with this drug and increase your risk of side effects.
  • Avoid taking Zyrtec with alcohol. Although cetirizine causes less drowsiness than a first-generation antihistamine, it can still make you drowsy. Drinking alcohol while you take it can increase this drowsiness.
  • Talk to your doctor before using Zyrtec if you have liver or kidney disease. Liver and kidney disease can both affect how your body processes and removes cetirizine.
  • You should also talk to your doctor before using Zyrtec if you have asthma. In rare cases, cetirizine has been shown to cause bronchospasms.

Claritin

Loratadine is the main active ingredient in Claritin. It helps relieve runny nose, sneezing, itchy, watery eyes, and itching of the nose or throat due to hay fever and other upper respiratory allergies. Claritin can also be used to treat hives. It comes in a tablet, a tablet that dissolves in your mouth, a chewable tablet, a liquid-filled capsule, and a syrup.

Loratadine is also the main active ingredient in these other OTC brands:

  • Claritin-D
  • Alavert
  • Alavert-D
  • Wal-itin

Side effects

Some of the common side effects of Claritin can include:

  • headache
  • drowsiness

Serious side effects of Claritin can include allergic reactions. Symptoms can include:

  • rash
  • itching
  • trouble breathing or swallowing
  • swelling of your face, throat, tongue, lips, eyes
  • hoarseness

Warnings

  • Talk to your doctor before using Claritin if you have liver or kidney disease. Liver and kidney disease can both affect how your body processes and removes loratadine. This can cause more of the drug to stay in your body and increase your risk of side effects.
  • You should also talk to your doctor before using Claritin if you have asthma. In rare cases, loratadine has been shown to cause bronchospasms.

Allegra

Fexofenadine is the main active ingredient in Allegra. It helps relieve runny nose, sneezing, itchy and watery eyes, and itching of the nose or throat due to hay fever or other upper respiratory allergies. Allegra can also be used to treat hives and skin rash. It comes in a tablet, a tablet that dissolves in your mouth, a gel-coated capsule, and a liquid.

Side effects

Some of the common side effects of Allegra can include:

  • headache
  • dizziness
  • diarrhea
  • vomiting
  • pain in your arms, legs, or back
  • pain during menstrual periods
  • cough
  • upset stomach

Serious side effects of Allegra can include allergic reaction. Symptoms include:

  • hives
  • rash
  • itching
  • trouble breathing or swallowing
  • swelling of your face, throat, tongue, lips, eyes

Warnings

  • Talk to your doctor before you use Allegra if you take the antifungal ketoconazole, the antibiotics erythromycin or rifampin, or any antacids. These drugs can all interact with Allegra to either increase your risk of side effects or decrease the effectiveness of Allegra.
  • Avoid drinking fruit juice while taking Allegra. Fruit juice can also decrease the amount of Allegra that your body absorbs. This can make the drug less effective.
  • If you have kidney disease, talk to your doctor before using Allegra. Kidney disease interferes with your body’s removal of Allegra. This can lead to an increased risk of side effects.

If you have allergies, you have a range of choices for OTC medications. These include brand-name antihistamines such as:

  • Benadryl
  • Chlor-Trimeton
  • Zyrtec
  • Claritin
  • Allegra

If you’re not sure which medication might be best for you, talk to your doctor or pharmacist. And if you take other medications to treat allergy symptoms, make sure that the active ingredients are not the same or in the same drug class as the active ingredient in the antihistamine you want to take. You don’t want to take too much of any particular drug. To help prevent this, always check with your doctor or pharmacist.

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