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Antihistamines

Medically reviewed by Carmen Pope, BPharm. Last updated on April 17, 2023.

What are Antihistamines?

Antihistamines block histamine release from histamine-1 receptors and are mostly used to treat allergies or cold and flu symptoms, although some first-generation antihistamines (also called sedating antihistamines) may be used for other conditions, such as nausea or motion sickness.

Histamine-1 receptors are located in your airways (breathing tubes), blood vessels, stomach, and esophagus (throat area). Allergens, such as pollen or pet fur can stimulate these receptors, causing the release of histamine, which results in symptoms such as a rash, sneezing, a runny nose, or a narrowing of the airways (also called bronchoconstriction). Histamine-1 receptors are also found in the brain and spinal cord and first-generation antihistamines (sedating antihistamines) can cross through the blood/brain barrier into the brain and act on these receptors, causing sleepiness (sedation), and drowsiness.

What are antihistamines used for?

Antihistamines can help relieve the symptoms of an allergic reaction, such as:

  • a rash
  • itchiness
  • redness (inflammation)
  • swelling (edema)
  • red and watery eyes
  • a runny nose
  • sneezing.

This makes antihistamines very effective for the treatment of:

Sedating antihistamines (see explanation below) also act in the brain and spinal cord, and on other receptors. This makes some of them also useful for:

  • inducing sleep
  • preventing or treating motion sickness
  • reducing anxiety
  • some symptoms of Parkinson’s disease in people unable to tolerate traditional medications for Parkinson's disease.

What are the differences between antihistamines?

Antihistamines can be classified into two main categories:

  • first-generation antihistamines (also known as sedating antihistamines because they all cause drowsiness)
  • second-generation antihistamines (also known as non-sedating antihistamines because they don't tend to cause drowsiness, although they may do so in some people).

First-generation (sedating) antihistamines were developed more than seventy years ago and are still in widespread use today. They act on histamine receptors in the brain and spinal cord and in the rest of the body (called the periphery). They also act on muscarinic, alpha-adrenergic, and serotonin receptors. This means that first-generation antihistamines are more likely to cause side effects such as sedation, dry mouth, dizziness, low blood pressure, and a rapid heart-beat. They are also more likely than second-generation antihistamines to impair a person’s ability to drive or operate machinery. Interactions with other drugs are more common with first-generation antihistamines compared with second-generation antihistamines.

Second generation (non-sedating) antihistamines were developed in the 1980s and are much less sedating than first-generation antihistamines. They act on histamine-1 receptors in the periphery and are unlikely to penetrate the brain, so are less likely to cause side effects or interact with drugs. Most second-generation antihistamines do not cause drowsiness, although some (such as cetirizine and fexofenadine), may be more likely to do so at higher dosages.

Common antihistamines available in the U.S.

First Generation (Sedating) Antihistamines

Generic name Brand name examples Duration of action
brompheniramine Generic 12h
carbinoxamine maleate Generic 12h
chlorpheniramine Aller-Chlor 24h
clemastine Generic 12h
diphenhydramine Benadryl 12h
hydroxyzine Vistaril 24h
triprolidine Discontinued 12h

Second Generation (Non-sedating) Antihistamines

What are the side effects of antihistamines?

Side effects of first-generation (sedating) antihistamines may include:

  • blurred or double vision
  • constipation
  • dry eyes
  • a dry mouth
  • drowsiness or sedation
  • a headache
  • low blood pressure
  • mucus thickening in the airways
  • a rapid heartbeat
  • stomach pain
  • urinary problems

Side effects of second-generation (non-sedating) antihistamines may include:

  • coughing
  • drowsiness (this is uncommon)
  • fatigue 
  • a headache
  • nausea
  • a sore throat
  • stomach pain.

List of Antihistamines

View by  Brand | Generic
Drug Name Avg. Rating Reviews
Xyzal (Pro)
Generic name: levocetirizine
5.4
289 reviews
Vistaril (Pro)
Generic name: hydroxyzine
5.6
232 reviews
Zyrtec (Pro)
Generic name: cetirizine
5.8
197 reviews
Phenergan (Pro)
Generic name: promethazine
7.3
147 reviews
Atarax (Pro)
Generic name: hydroxyzine
6.2
146 reviews
Nytol
Generic name: diphenhydramine
4.0
140 reviews
Allegra (Pro)
Generic name: fexofenadine
6.8
93 reviews
Benadryl (Pro)
Generic name: diphenhydramine
7.3
78 reviews
Sominex
Generic name: diphenhydramine
6.3
64 reviews
Claritin (Pro)
Generic name: loratadine
3.5
49 reviews
Benadryl Allergy (Pro)
Generic name: diphenhydramine
7.0
30 reviews
Unisom SleepGels
Generic name: diphenhydramine
4.9
21 reviews
Simply Sleep
Generic name: diphenhydramine
5.2
20 reviews
Chlor-Trimeton (Pro)
Generic name: chlorpheniramine
8.8
18 reviews
Allegra Allergy (Pro)
Generic name: fexofenadine
3.3
10 reviews
Seldane
Generic name: terfenadine
10
7 reviews
Clarinex (Pro)
Generic name: desloratadine
7.3
6 reviews
Polaramine
Generic name: dexchlorpheniramine
7.4
5 reviews
Hyzine
Generic name: hydroxyzine
6.0
3 reviews
Children's Claritin Allergy
Generic name: loratadine
8.3
3 reviews
Alavert (Pro)
Generic name: loratadine
9.7
3 reviews
Wal-itin
Generic name: loratadine
6.0
2 reviews
Unisom SleepMelts
Generic name: diphenhydramine
9.0
2 reviews
Palgic
Generic name: carbinoxamine
9.0
2 reviews
Compoz Nighttime Sleep Aid
Generic name: diphenhydramine
9.0
2 reviews
Banophen
Generic name: diphenhydramine
9.5
2 reviews
Allegra ODT
Generic name: fexofenadine
10
2 reviews
Wal-finate
Generic name: chlorpheniramine
9.0
1 review
Promethegan (Pro)
Generic name: promethazine
1 review
Phenadoz
Generic name: promethazine
8.0
1 review
Diphen
Generic name: diphenhydramine
10
1 review
Benadryl Children's Allergy
Generic name: diphenhydramine
10
1 review
Aller-Tec
Generic name: cetirizine
10
1 review
Aller-Ease
Generic name: fexofenadine
1.0
1 review
All Day Allergy
Generic name: cetirizine
9.0
1 review
Vanahist PD
Generic name: triprolidine
No reviews
Vanaclear PD
Generic name: triprolidine
No reviews
Valu-Dryl
Generic name: diphenhydramine
No reviews
Twilite
Generic name: diphenhydramine
No reviews
Triaminic Thin Strips Cough & Runny Nose
Generic name: diphenhydramine
No reviews
Tavist ND
Generic name: loratadine
No reviews
Tavist Allergy
Generic name: clemastine
No reviews
Sleepinal
Generic name: diphenhydramine
No reviews
Sleep-ettes D
Generic name: diphenhydramine
No reviews
Silphen Cough
Generic name: diphenhydramine
No reviews
Siladryl Allergy
Generic name: diphenhydramine
No reviews
Scot-Tussin Allergy
Generic name: diphenhydramine
No reviews
Ryvent (Pro)
Generic name: carbinoxamine
No reviews
Ryclora (Pro)
Generic name: dexchlorpheniramine
No reviews
Quzyttir (Pro)
Generic name: cetirizine
No reviews
Polmon
Generic name: dexchlorpheniramine
No reviews
Pediox
Generic name: carbinoxamine
No reviews
Pediatex
Generic name: carbinoxamine
No reviews
PediaTan
Generic name: chlorpheniramine
No reviews
ohm Allergy Relief
Generic name: loratadine
No reviews
M-Hist PD
Generic name: triprolidine
No reviews
Karbinal ER (Pro)
Generic name: carbinoxamine
No reviews
Histex Syrup
Generic name: triprolidine
No reviews
Histex PD Drops
Generic name: triprolidine
No reviews
Histex PD
Generic name: carbinoxamine
No reviews
Histex IE
Generic name: carbinoxamine
No reviews
Histex CT
Generic name: carbinoxamine
No reviews
Histex
Generic name: triprolidine
No reviews
Ed Chlor Ped Jr.
Generic name: chlorpheniramine
No reviews
Ed ChlorPed
Generic name: chlorpheniramine
No reviews
Ed-Chlortan
Generic name: chlorpheniramine
No reviews
Dytuss
Generic name: diphenhydramine
No reviews
Dormin
Generic name: diphenhydramine
No reviews
Diphenhist
Generic name: diphenhydramine
No reviews
Diphedryl
Generic name: diphenhydramine
No reviews
Dimetapp Children's ND Non-Drowsy Allergy
Generic name: loratadine
No reviews
Dicopanol
Generic name: diphenhydramine
No reviews
Complete Allergy Relief
Generic name: diphenhydramine
No reviews
Claritin Reditabs
Generic name: loratadine
No reviews
Clarinex Reditabs
Generic name: desloratadine
No reviews
ChlorTan
Generic name: chlorpheniramine
No reviews
Chlor-Mal
Generic name: chlorpheniramine
No reviews
Chlo-Amine
Generic name: chlorpheniramine
No reviews
Carboxine
Generic name: carbinoxamine
No reviews
C.P.M.
Generic name: chlorpheniramine
No reviews
Bromax
Generic name: brompheniramine
No reviews
Arbinoxa
Generic name: carbinoxamine
No reviews
Antinaus 50
Generic name: promethazine
No reviews
Allermax
Generic name: diphenhydramine
No reviews
Allergy Relief Tablets
Generic name: loratadine
No reviews
Allergy Relief 24 Hour
Generic name: loratadine
No reviews
Allergy Relief
Generic name: chlorpheniramine
No reviews
Aller-Tec Children's
Generic name: cetirizine
No reviews
Aller-Chlor
Generic name: chlorpheniramine
No reviews
Allegra Hives
Generic name: fexofenadine
No reviews
All Day Allergy Children's
Generic name: cetirizine
No reviews
Ala-Hist IR
Generic name: dexbrompheniramine
No reviews
For ratings, users were asked how effective they found the medicine while considering positive/adverse effects and ease of use (1 = not effective, 10 = most effective).

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.