Antihistamines: Relief for Allergies, Sleepless Nights, and More

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A person with allergy symptoms rubbing their itchy eyes. Relief is on the way with antihistamines.


Antihistamines are medications commonly used to alleviate symptoms of allergies by blocking histamine, a substance in the body responsible for allergic reactions. They come in two main types: first-generation, which can cause drowsiness, and second-generation, which are less likely to induce drowsiness. Common uses include treating allergic rhinitis, hives, and motion sickness, though caution is advised when operating machinery or combining them with alcohol due to potential side effects like drowsiness and dry mouth. It’s important to consult healthcare providers about potential interactions with other medications and to discuss long-term use for managing chronic conditions.

In this blog, we discuss these topics 

What is Antihistamines

Antihistamines are medications commonly used to alleviate allergy symptoms, including hay fever, hives, conjunctivitis, and reactions to insect bites or stings. Additionally, they can be utilized to prevent motion sickness, treat nausea and vomiting, and serve as a short-term solution for insomnia. While many antihistamines are available over the counter at pharmacies and stores, some require a prescription.

Antihistamine types

Antihistamines are classified into two main types: first-generation and second-generation.

First-Generation Antihistamines

These are older and tend to cause more side effects, such as drowsiness and dry mouth. They are often used for their sedative properties and are effective for treating symptoms of allergies, motion sickness, nausea, and insomnia. Common first-generation antihistamines include:

  • Diphenhydramine (Benadryl)
  • Chlorpheniramine (Chlor-Trimeton)
  • Hydroxyzine (Atarax, Vistaril)
  • Dimenhydrinate (Dramamine)
  • Meclizine (Antivert, Bonine)

Second-Generation Antihistamines

These are newer and generally cause fewer side effects, particularly less drowsiness, making them more suitable for daytime use. They are primarily used for treating allergy symptoms. Common second-generation antihistamines include:

  • Cetirizine (Zyrtec)
  • Loratadine (Claritin)
  • Fexofenadine (Allegra)
  • Desloratadine (Clarinex)
  • Levocetirizine (Xyzal)

Each type has its specific uses and benefits, so the choice of antihistamine can depend on the individual’s symptoms and lifestyle.

Different types of antihistamine medications in blister packs and pill bottles on a pharmacy shelf.

Which one is the best?

Determining the “best” antihistamine depends on the individual’s specific needs, symptoms, and response to the medication. Here are some considerations for choosing the most suitable antihistamine:

First-Generation vs. Second-Generation

  • First-Generation Antihistamines: These are effective for severe allergic reactions and can also help with nausea, vomiting, and insomnia due to their sedative effects. However, they often cause drowsiness and other side effects. Examples include diphenhydramine and chlorpheniramine.
  • Second-generation antihistamines: These are preferred for daily allergy relief as they cause less drowsiness and have fewer side effects. They are effective for treating hay fever, hives, and other allergic conditions. Examples include cetirizine, loratadine, and fexofenadine.

Specific Recommendations

  • Cetirizine (Zyrtec): Known for its fast action and effectiveness in treating a wide range of allergy symptoms, but it can cause some drowsiness in a minority of users.
  • Loratadine (Claritin): Less likely to cause drowsiness and is a good choice for those needing to stay alert.
  • Fexofenadine (Allegra): This is the least likely to cause drowsiness and is effective for long-lasting allergy relief.
  • Diphenhydramine (Benadryl): Highly effective for severe allergic reactions and also useful as a short-term sleep aid, but it causes significant drowsiness.

Personal Considerations

  • Lifestyle: If you need to remain alert and active during the day, a second-generation antihistamine like loratadine or fexofenadine is a better choice.
  • Severity of Symptoms: For severe allergic reactions or if you need help with sleep, a first-generation antihistamine like diphenhydramine might be more appropriate.
  • Side Effects: Consider your tolerance for potential side effects like drowsiness or dry mouth.

Ultimately, the “best” antihistamine is the one that effectively manages your symptoms with the fewest side effects. Try a few different options to determine which works best for you. Consulting with a healthcare provider can also help in making an informed decision based on your health profile and specific needs.

How antihistamines are taken

Antihistamines come in various forms and can be taken in different ways, depending on the type and intended use. Here are the common methods of administration:


  1. Tablets and Capsules: Swallowed with water; often taken once or twice daily.
  • Example: Cetirizine (Zyrtec), Loratadine (Claritin)
  1. Chewable Tablets: Chewed before swallowing; convenient for children or those who have difficulty swallowing pills.
  • Example: Loratadine chewable tablets
  1. Liquid Syrups: Measured with a dosing spoon or cup; often used for children or people who have difficulty swallowing tablets.
  • Example: Diphenhydramine (Benadryl) syrup


  1. Creams and Lotions: Applied directly to the skin to relieve itching and hives.
  • Example: Diphenhydramine cream
  1. Gels: Similar to creams and lotions but with a gel consistency for easy application.
  • Example: Diphenhydramine gel


  1. Nasal Sprays: Sprayed into each nostril to relieve nasal congestion and other allergy symptoms.
  • Example: Azelastine (Astelin)


  1. Eye Drops: Instilled into the eyes to relieve symptoms of allergic conjunctivitis, such as itching and redness.
  • Example: Ketotifen (Zaditor), Olopatadine (Patanol)


  1. Injections: Administered by a healthcare professional for severe allergic reactions, such as anaphylaxis.
  • Example: Diphenhydramine injection

Usage Instructions

  • Follow Dosage Recommendations: Always adhere to the prescribed or recommended dosage on the packaging or as directed by a healthcare provider.
  • Timing: Some antihistamines are taken once daily, while others may be taken more frequently. Follow the specific instructions for timing and frequency.
  • With or Without Food: Some antihistamines should be taken with food to prevent stomach upset, while others can be taken on an empty stomach. Check the label or ask a healthcare provider.
  • Measure Liquid Doses Accurately: Use the provided measuring device (spoon, cup, or syringe) to ensure the correct dose.

Antihistamine side effects

Antihistamines can cause various side effects, which can differ depending on whether they are first-generation or second-generation antihistamines. Here are some common side effects:

First-Generation Antihistamines

These are more likely to cause side effects due to their ability to cross the blood-brain barrier.

  • Drowsiness: This is the most common side effect, making these antihistamines useful as sleep aids but problematic for daytime use.
  • Dry Mouth and Throat: Anticholinergic effects can lead to a dry sensation in the mouth and throat.
  • Dizziness: Feeling lightheaded or unsteady.
  • Constipation: Reduced bowel movements due to the anticholinergic effects.
  • Urinary Retention: Difficulty urinating.
  • Blurred Vision: Difficulty focusing on objects.
  • Confusion and Memory Problems: Particularly in older adults.

Second-Generation Antihistamines

These are designed to minimize drowsiness and other central nervous system effects.

  • Drowsiness: Less common but can still occur, especially with cetirizine.
  • Headache: A potential side effect in some individuals.
  • Dry Mouth: Less pronounced than with first-generation antihistamines.
  • Nausea: Mild stomach upset in some users.
  • Fatigue: Feeling unusually tired or weak.
  • Dizziness: Although less common, it can still occur.

Rare but Serious Side Effects

  • Allergic Reactions: Hives, rash, itching, swelling of the face or throat, severe dizziness, and trouble breathing.
  • Heart Palpitations: Irregular or fast heartbeats, particularly with higher doses or in susceptible individuals.
  • Seizures: Rare but possible, especially in predisposed individuals or with overdose.
  • Severe Drowsiness: This leads to significant impairment, especially when combined with alcohol or other sedatives.

Workings of antihistamines

Antihistamines work by blocking the effects of histamine, a substance produced by the body during an allergic reaction. Here’s a detailed look at how they function:

Histamine and Its Role

  • Histamine Release: When the body encounters an allergen (such as pollen, pet dander, or dust mites), the immune system reacts by releasing histamine from mast cells and basophils.
  • Histamine Effects: Histamine binds to histamine receptors, particularly H1 receptors, causing symptoms like itching, swelling, redness, mucus production, and bronchoconstriction.

Mechanism of Action

  • Histamine Receptors: Histamine primarily acts on H1 receptors (involved in allergic responses) and H2 receptors (involved in gastric acid secretion). Antihistamines used for allergies mainly target H1 receptors.
  • Blocking Histamine: Antihistamines are H1 receptor antagonists, meaning they bind to these receptors without activating them, effectively blocking histamine from exerting its effects.

First-Generation Antihistamines

  • Crossing the Blood-Brain Barrier: These antihistamines can cross the blood-brain barrier, leading to central nervous system (CNS) effects, such as drowsiness and sedation.
  • Examples: Diphenhydramine, chlorpheniramine, hydroxyzine.

Second-Generation Antihistamines

  • Limited CNS Penetration: These drugs are designed to not easily cross the blood-brain barrier, reducing drowsiness and other CNS side effects.
  • Selective Action: They selectively block peripheral H1 receptors.
  • Examples: Cetirizine, loratadine, fexofenadine.


Q1. What are antihistamines used for?

A1. Antihistamines are medicines that help with allergies and can also help with stomach issues, colds, anxiety, and more. They work by reducing histamine, a chemical your body makes when you have an allergic reaction.

Q2. What is the best antihistamine?

A2. Doctors recommend long-lasting, non-drowsy antihistamines for everyday use. Some good ones are:

Cetirizine (Zyrtec®, Aller-Tec®, Wall-Zyr®)

Fexofenadine (Allegra®, Aller-ease®, Aller-Fex®, Wal-Fex®)

Q3. Is antihistamine a steroid?

A3. No, antihistamines and steroids are different. Antihistamines reduce histamine to help with allergies, while steroids reduce inflammation caused by chronic conditions.

Q4. What is a powerful antihistamine?

A4. Cetirizine is considered one of the strongest antihistamines and has been studied a lot.

Q5. Antihistamine safe?

A5. Yes, antihistamines are usually safe for most people, including adults, kids over 2, and older people. If you are pregnant, breastfeeding, or have a long-term illness, check with your doctor before using antihistamines.

Q6. What is the fastest allergy relief?

A6. Decongestants: These work the fastest. Nasal sprays work in about 10 minutes, and pills work in 30 to 60 minutes. Oral antihistamines: These also work quickly, usually within 1 to 2 hours.

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