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Antihistamines

What are Antihistamines?

Antihistamines are a class of agents that block histamine release from histamine-1 receptors and are mostly used to treat allergies or cold and flu symptoms, although some first-generation antihistamines may also be used for other conditions.

Histamine-1 receptors are located in the airways, blood vessels and gastrointestinal tract (stomach and esophagus). Histamine-1 receptors are also found in the brain and spinal cord.

What are antihistamines used for?

Antihistamines are very good at relieving symptoms of an allergic reaction, such as:

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

This makes antihistamines very effective in the treatment of:

First generation 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
  • in people with Parkinson’s disease unable to tolerate more potent agents.

What are the differences between antihistamines?

Antihistamines can be classified into two main categories:

  • first-generation antihistamines
  • second-generation antihistamines.

First-generation 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 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 Antihistamines

Second Generation Antihistamines

What are the side effects of antihistamines?

Side effects of first-generation antihistamines may include:

  • abdominal pain
  • 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 heart beat
  • urinary problems

Side effects of second generation antihistamines are uncommon but may include:

List of Antihistamines:

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Drug NameView by: Brand | Generic Reviews Avg. Ratings
Allegra ODT (More...)
generic name: fexofenadine
1 review
   
10
Seldane (More...)
generic name: terfenadine
3 reviews
   
10
Zymine (More...)
generic name: triprolidine
1 review
   
9.7
Chlor-Trimeton (Pro, More...)
generic name: chlorpheniramine
12 reviews
   
9.1
All Day Allergy (Pro, More...)
generic name: cetirizine
1 review
   
9.0
Compoz Nighttime Sleep Aid (More...)
generic name: diphenhydramine
2 reviews
   
9.0
Palgic (Pro, More...)
generic name: carbinoxamine
2 reviews
   
9.0
Q-Dryl (More...)
generic name: diphenhydramine
1 review
   
9.0
Unisom SleepMelts (More...)
generic name: diphenhydramine
1 review
   
9.0
Wal-finate (More...)
generic name: chlorpheniramine
1 review
   
9.0
Promethegan (Pro, More...)
generic name: promethazine
0 reviews
   
8.4
Children's Claritin Allergy (More...)
generic name: loratadine
3 reviews
   
8.3
Phenergan (Pro, More...)
generic name: promethazine
86 reviews
   
8.3
Benadryl Children's Allergy (More...)
generic name: diphenhydramine
0 reviews
   
8.0
Antinaus 50 (More...)
generic name: promethazine
0 reviews
   
7.7
Benadryl (Pro, More...)
generic name: diphenhydramine
45 reviews
   
7.5
Clarinex (Pro, More...)
generic name: desloratadine
5 reviews
   
7.5
Allegra (Pro, More...)
generic name: fexofenadine
66 reviews
   
7.4
Benadryl Allergy (More...)
generic name: diphenhydramine
26 reviews
   
7.4
Zyrtec (Pro, More...)
generic name: cetirizine
113 reviews
   
7.2
Allerhist-1 (More...)
generic name: clemastine
0 reviews
   
7.0
Banophen (More...)
generic name: diphenhydramine
0 reviews
   
7.0
Polaramine (More...)
generic name: dexchlorpheniramine
3 reviews
   
7.0
Sominex (More...)
generic name: diphenhydramine
23 reviews
   
6.7
Atarax (Pro, More...)
generic name: hydroxyzine
95 reviews
   
6.5
Phenadoz (Pro, More...)
generic name: promethazine
0 reviews
   
6.5
Xyzal (Pro, More...)
generic name: levocetirizine
170 reviews
   
6.5
Lodrane 12 Hour (More...)
generic name: brompheniramine
0 reviews
   
6.0
Vistaril (Pro, More...)
generic name: hydroxyzine
163 reviews
   
5.8
Nytol (More...)
generic name: diphenhydramine
7 reviews
   
5.7
Alavert (Pro, More...)
generic name: loratadine
1 review
   
5.5
Hyzine (More...)
generic name: hydroxyzine
2 reviews
   
5.5
Unisom SleepGels (More...)
generic name: diphenhydramine
14 reviews
   
5.4
Simply Sleep (More...)
generic name: diphenhydramine
13 reviews
   
5.2
Claritin (Pro, More...)
generic name: loratadine
18 reviews
   
5.1
Tavist (More...)
generic name: clemastine
1 review
   
5.0
Triaminic Thin Strips Cough & Runny Nose (More...)
generic name: diphenhydramine
0 reviews
   
3.0
Allegra Allergy (More...)
generic name: fexofenadine
6 reviews
   
2.9
Aller-Ease (More...)
generic name: fexofenadine
1 review
   
1.0
Vicks QlearQuil Nighttime Allergy Relief (More...)
generic name: diphenhydramine
1 review
   
1.0
12 Hour Allergy Relief (More...)
generic name: clemastine
0 reviewsAdd rating
Ala-Hist IR (More...)
generic name: dexbrompheniramine
0 reviewsAdd rating
All Day Allergy Children's (Pro, More...)
generic name: cetirizine
0 reviewsAdd rating
Aller-Chlor (More...)
generic name: chlorpheniramine
0 reviewsAdd rating
Aller-Tec (More...)
generic name: cetirizine
0 reviewsAdd rating
Aller-Tec Children's (More...)
generic name: cetirizine
0 reviewsAdd rating
Allergy Relief (More...)
generic name: chlorpheniramine
0 reviewsAdd rating
Allergy Relief 24 Hour (More...)
generic name: loratadine
0 reviewsAdd rating
Allergy Relief Tablets (More...)
generic name: loratadine
0 reviewsAdd rating
Allermax (More...)
generic name: diphenhydramine
0 reviewsAdd rating
Arbinoxa (Pro, More...)
generic name: carbinoxamine
0 reviewsAdd rating
Bactimicina Allergy (More...)
generic name: loratadine
0 reviewsAdd rating
Bromax (Pro, More...)
generic name: brompheniramine
0 reviewsAdd rating
Brovex CT (More...)
generic name: brompheniramine
0 reviewsAdd rating
C.P.M. (More...)
generic name: chlorpheniramine
0 reviewsAdd rating
Carboxine (More...)
generic name: carbinoxamine
0 reviewsAdd rating
Children's Allergy Relief (More...)
generic name: cetirizine
0 reviewsAdd rating
Children's Allergy Relief 24 Hour (More...)
generic name: loratadine
0 reviewsAdd rating
Chlo-Amine (More...)
generic name: chlorpheniramine
0 reviewsAdd rating
Chlor-Mal (More...)
generic name: chlorpheniramine
0 reviewsAdd rating
ChlorTan (More...)
generic name: chlorpheniramine
0 reviewsAdd rating
Clarinex Reditabs (More...)
generic name: desloratadine
0 reviewsAdd rating
Claritin Reditabs (More...)
generic name: loratadine
0 reviewsAdd rating
Clear-Atadine (More...)
generic name: loratadine
0 reviewsAdd rating
Complete Allergy Relief (More...)
generic name: diphenhydramine
0 reviewsAdd rating
Dayhist Allergy (More...)
generic name: clemastine
0 reviewsAdd rating
Dicopanol (More...)
generic name: diphenhydramine
0 reviewsAdd rating
Dimetane Extentab (More...)
generic name: brompheniramine
0 reviewsAdd rating
Dimetapp Children's ND Non-Drowsy Allergy (Pro, More...)
generic name: loratadine
0 reviewsAdd rating
Diphedryl (More...)
generic name: diphenhydramine
0 reviewsAdd rating
Diphenhist (More...)
generic name: diphenhydramine
0 reviewsAdd rating
Dytuss (More...)
generic name: diphenhydramine
0 reviewsAdd rating
Ed-Chlortan (More...)
generic name: chlorpheniramine
0 reviewsAdd rating
Ed ChlorPed (More...)
generic name: chlorpheniramine
0 reviewsAdd rating
Ed Chlor Ped Jr. (More...)
generic name: chlorpheniramine
0 reviewsAdd rating
Histex CT (More...)
generic name: carbinoxamine
0 reviewsAdd rating
Histex IE (More...)
generic name: carbinoxamine
0 reviewsAdd rating
Histex PD (More...)
generic name: carbinoxamine
0 reviewsAdd rating
Histex PD Drops (More...)
generic name: triprolidine
0 reviewsAdd rating
Histex Syrup (More...)
generic name: triprolidine
0 reviewsAdd rating
J-Tan PD (More...)
generic name: brompheniramine
0 reviewsAdd rating
Karbinal ER (Pro, More...)
generic name: carbinoxamine
0 reviewsAdd rating
Leader Allerhist (More...)
generic name: clemastine
0 reviewsAdd rating
LoHist-12 (More...)
generic name: brompheniramine
0 reviewsAdd rating
M-Hist PD (More...)
generic name: triprolidine
0 reviewsAdd rating
ohm Allergy Relief (More...)
generic name: loratadine
0 reviewsAdd rating
PediaCare Children's Allergy (More...)
generic name: diphenhydramine
0 reviewsAdd rating
PediaTan (More...)
generic name: chlorpheniramine
0 reviewsAdd rating
Pediatex (More...)
generic name: carbinoxamine
0 reviewsAdd rating
Pediox (More...)
generic name: carbinoxamine
0 reviewsAdd rating
Quenalin (More...)
generic name: diphenhydramine
0 reviewsAdd rating
Ryvent (Pro, More...)
generic name: carbinoxamine
0 reviewsAdd rating
Scot-Tussin Allergy (More...)
generic name: diphenhydramine
0 reviewsAdd rating
Siladryl Allergy (More...)
generic name: diphenhydramine
0 reviewsAdd rating
Silphen Cough (More...)
generic name: diphenhydramine
0 reviewsAdd rating
Siltane (More...)
generic name: brompheniramine
0 reviewsAdd rating
Sleepinal (More...)
generic name: diphenhydramine
0 reviewsAdd rating
Tavist-1 (More...)
generic name: clemastine
0 reviewsAdd rating
Tavist Allergy (More...)
generic name: clemastine
0 reviewsAdd rating
Tavist ND (More...)
generic name: loratadine
0 reviewsAdd rating
Topco Allergy (More...)
generic name: chlorpheniramine
0 reviewsAdd rating
Tranquil Nighttime Sleep Aid (More...)
generic name: diphenhydramine
0 reviewsAdd rating
Tripohist (More...)
generic name: triprolidine
0 reviewsAdd rating
Twilite (More...)
generic name: diphenhydramine
0 reviewsAdd rating
Valu-Dryl (More...)
generic name: diphenhydramine
0 reviewsAdd rating
Vanaclear PD (More...)
generic name: triprolidine
0 reviewsAdd rating
Vanahist PD (More...)
generic name: triprolidine
0 reviewsAdd rating
VaZol (More...)
generic name: brompheniramine
0 reviewsAdd rating
Vicks QlearQuil All Day & All Night 24 Hour Allergy Relief (More...)
generic name: loratadine
0 reviewsAdd rating
Wal-itin (More...)
generic name: loratadine
0 reviewsAdd rating
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