Antihistamine: Which One Is Best For Me?

Each year, nearly 1 in 4 adults in the United States suffer from seasonal allergies. If you're one of them, you're likely familiar with the relentless sneezing, itchy eyes, and runny nose that allergens like pollen, dust, and pet dander can trigger. For millions, antihistamines are a go-to solution, with popular choices like Benadryl, Zyrtec, and Claritin offering relief. But not all antihistamines are created equal.

From different formulations to varying side effects, choosing the right antihistamine can make a difference in how effectively you manage your symptoms. In this blog, we'll break down the key differences between common antihistamines, explore how they work, and guide you toward finding the one that suits your needs.

How Antihistamines Work

Antihistamines are frequently used to alleviate your allergy symptoms. They work by blocking histamine at the histamine-1 (H1) receptor site. This drug class can help if you have symptoms of allergic conjunctivitis, such as itchy or red eyes, are present.

Antihistamines administered orally are widely used for mild to moderate symptoms. They have limited impact on nasal congestion but are beneficial in reducing itching, sneezing, and runny nose, and may only take approximately 1 to 3 hours to start working.

Antihistamines can be used beforehand to prevent seasonal allergies before exposure to an allergen trigger, such as pollen. For optimal benefits, start the drug at least 2 weeks before allergy season starts. If you experience seasonal allergy problems frequently, this may be especially beneficial.

There are 2 types of antihistamines: first-generation and second-generation. First-generation antihistamines tend to cause drowsiness and are often used at bedtime or only when symptoms are particularly bad. Second-generation antihistamines are preferred for daily use because they are non-drowsy and provide longer-lasting relief, usually taken once a day.

First Generation Antihistamines

First-generation antihistamines are often effective for managing allergy symptoms but come with a higher risk of side effects compared to newer medications. These drugs are generally not recommended for lactating women, who should instead opt for second-generation antihistamines.

• Diphenhydramine HCL (Benadryl)
  • Adults: 25-50 mg taken orally every 4 to 6 hours
  • Children (6-11 years): 12.5-25 mg taken orally every 4 to 6 hours
  • Uses: Diphenhydramine is versatile, often used for acute allergic reactions, allergy prevention, nasal congestion, cough, sleep aid, and motion sickness.
• Clemastine (Dayhist Allergy 12 HR Relief)
  • Dose: 1.34-2.68 mg taken every 8 to 12 hours
• Carbinoxamine (Karbinal ER, RyVent)
  • Immediate-release (IR): 4-8 mg every 6 to 12 hours for adults
  • Extended-release (ER): 6-16 mg every 12 hours for adults
• Chlorpheniramine
  • IR: 4 mg every 4 to 6 hours
  • ER: 12 mg every 12 hours

Common Side Effects of First-Generation Antihistamines

• Sleepiness: These medications often cause drowsiness, which can interfere with daily activities.
• Cognitive Impairment: Difficulty concentrating or slowed reaction times may occur.
• Dry Mouth: This is a frequent side effect, often accompanied by a feeling of thirst.
• Blurred Vision: Some people may experience changes in their vision.
• Urinary Retention: Difficulty urinating may arise, especially in men with prostate issues.
• Constipation: Slowed digestion is another common side effect.
• Seizures and Increased Heart Rate: While rare, high doses can lead to more severe issues such as seizures or a rapid heartbeat.

Second-Generation Antihistamines: A Safer, Non-Drowsy Option for Allergy Relief

Second-generation antihistamines work by binding to histamine receptors in the brain and spinal cord, effectively blocking the release of histamine, a chemical responsible for triggering allergic reactions. Excess histamine in the body can cause symptoms such as:

• Swelling
• Irregular heart rate
• Bronchial constriction
• Smooth muscle contraction
• Lowered blood pressure

These newer antihistamines were developed to be safer and more effective for daily use. A major advantage of second-generation antihistamines is that they do not cross the blood-brain barrier, which significantly reduces the risk of drowsiness and cognitive impairment. This makes them a better option for people who need symptom relief while staying alert throughout the day.

• Cetirizine (Zyrtec)
  • Adults: 5-10 mg taken orally once daily
  • Children (2-5 years): 2.5-5 mg taken orally once daily
  • Uses: Treats both seasonal and year-round allergies.
  • Onset and Duration: Cetirizine starts working within about 1 hour and provides relief for up to 24 hours.
• Fexofenadine (Allegra)
  • Adults: 60 mg taken twice daily or 180 mg once daily
  • Children (2-11 years): 30 mg taken twice daily
  • Important Note: Fexofenadine should be taken with water, as juice can interfere with absorption.
  • Uses: Effective for both seasonal and year-round allergies.
  • Onset and Duration: It takes about 2 hours to start working, with effects lasting up to 24 hours.
  • Possible Side Effects: Headache, fatigue, dizziness, and dry mouth.
• Loratadine (Claritin)
  • Adults: 10 mg once daily or 5 mg twice daily
  • Children (2-5 years): 5 mg once daily
  • Uses: Treats both seasonal and year-round allergies.
  • Onset and Duration: It begins working within 1 to 3 hours, with relief lasting up to 24 hours.
  • Possible Side Effects: Weakness, sleepiness, abdominal pain, dizziness, and dry mouth.
• Levocetirizine (Xyzal Allergy 24HR)
  • Adults: 5 mg taken orally at night
  • Children (6-11 years): 2.5 mg at night
  • Children (6 months-5 years): 1.25 mg at night
  • Uses: Effective for evening relief of allergy symptoms.
  • Possible Side Effects: Tiredness is the most common side effect.

Second-generation antihistamines provide a safer, more convenient option for managing allergies. Their longer-lasting effects, reduced sedative properties, and ability to be used daily make them ideal for individuals seeking effective symptom relief without the side effects of earlier medications.