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Antihistamines

Medically reviewed by C. Fookes, BPharm. Last updated on Feb 5, 2019.

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). Stimulation of these receptors can lead to conditions such as a skin rash or inflammation, a narrowing of the airways (bronchoconstriction), hay fever, or motion sickness. Histamine-1 receptors are also found in the brain and spinal cord, and stimulation of these receptors makes you more awake and alert. Sedating antihistamines oppose the effects of histamine on H1 receptors in your brain, which is why they cause sedation and drowsiness.

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
  • a 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

Generic name Brand name Duration of action
brompheniramine Bromax, Lodrane 12-Hour 12h
carbinoxamine maleate Karbinal ER Oral Suspension 12h
chlorpheniramine Chlor-Trimeton 24h
clemastine Tavist Allergy 12h
diphenhydramine Benadryl 12h
hydroxyzine Atarax, Vistaril 24h
triprolidine Tripohist 12h

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 heartbeat
  • urinary problems

Side effects of second-generation antihistamines may include:

List of Antihistamines:

View by  Brand | Generic
Drug Name Reviews Avg. Ratings
Allegra ODT
Generic name: fexofenadine
1 review
10
Aller-Tec
Generic name: cetirizine
1 review
10
Seldane
Generic name: terfenadine
4 reviews
10
Wal-itin
Generic name: loratadine
1 review
10
Chlor-Trimeton (Pro)
Generic name: chlorpheniramine
14 reviews
9.1
All Day Allergy
Generic name: cetirizine
1 review
9.0
Benadryl Children's Allergy
Generic name: diphenhydramine
1 review
9.0
Compoz Nighttime Sleep Aid
Generic name: diphenhydramine
2 reviews
9.0
Palgic (Pro)
Generic name: carbinoxamine
2 reviews
9.0
Wal-finate
Generic name: chlorpheniramine
1 review
9.0
Promethegan (Pro)
Generic name: promethazine
1 review
8.4
Phenergan (Pro)
Generic name: promethazine
116 reviews
7.8
Antinaus 50
Generic name: promethazine
0 reviews
7.7
Clarinex (Pro)
Generic name: desloratadine
5 reviews
7.5
Benadryl (Pro)
Generic name: diphenhydramine
59 reviews
7.3
Allegra (Pro)
Generic name: fexofenadine
86 reviews
7.1
Polaramine
Generic name: dexchlorpheniramine
3 reviews
7.0
Alavert (Pro)
Generic name: loratadine
3 reviews
6.8
Phenadoz (Pro)
Generic name: promethazine
0 reviews
6.5
Zyrtec (Pro)
Generic name: cetirizine
161 reviews
6.5
Atarax (Pro)
Generic name: hydroxyzine
130 reviews
6.4
Sominex
Generic name: diphenhydramine
50 reviews
6.4
Xyzal (Pro)
Generic name: levocetirizine
250 reviews
5.9
Vistaril (Pro)
Generic name: hydroxyzine
208 reviews
5.6
Hyzine
Generic name: hydroxyzine
2 reviews
5.5
Unisom SleepGels
Generic name: diphenhydramine
19 reviews
5.2
Simply Sleep
Generic name: diphenhydramine
19 reviews
5.1
Claritin (Pro)
Generic name: loratadine
31 reviews
5.0
Sleepinal
Generic name: diphenhydramine
0 reviews
5.0
Allegra Allergy
Generic name: fexofenadine
8 reviews
2.7
Aller-Ease
Generic name: fexofenadine
1 review
1.0
12 Hour Allergy Relief
Generic name: clemastine
0 reviewsAdd rating
Ala-Hist IR
Generic name: dexbrompheniramine
0 reviewsAdd rating
All Day Allergy Children's
Generic name: cetirizine
0 reviewsAdd rating
Aller-Chlor
Generic name: chlorpheniramine
0 reviewsAdd rating
Aller-Tec Children's
Generic name: cetirizine
0 reviewsAdd rating
Allergy Relief
Generic name: chlorpheniramine
0 reviewsAdd rating
Allergy Relief 24 Hour
Generic name: loratadine
0 reviewsAdd rating
Allergy Relief Tablets
Generic name: loratadine
0 reviewsAdd rating
Allermax
Generic name: diphenhydramine
0 reviewsAdd rating
Arbinoxa (Pro)
Generic name: carbinoxamine
0 reviewsAdd rating
Bactimicina Allergy
Generic name: loratadine
0 reviewsAdd rating
Bromax
Generic name: brompheniramine
0 reviewsAdd rating
C.P.M.
Generic name: chlorpheniramine
0 reviewsAdd rating
Carboxine
Generic name: carbinoxamine
0 reviewsAdd rating
Children's Allergy Relief
Generic name: cetirizine
0 reviewsAdd rating
Children's Allergy Relief 24 Hour
Generic name: loratadine
0 reviewsAdd rating
Chlo-Amine
Generic name: chlorpheniramine
0 reviewsAdd rating
Chlor-Mal
Generic name: chlorpheniramine
0 reviewsAdd rating
ChlorTan
Generic name: chlorpheniramine
0 reviewsAdd rating
Clarinex Reditabs
Generic name: desloratadine
0 reviewsAdd rating
Claritin Reditabs
Generic name: loratadine
0 reviewsAdd rating
Clear-Atadine
Generic name: loratadine
0 reviewsAdd rating
Dayhist Allergy
Generic name: clemastine
0 reviewsAdd rating
Dicopanol
Generic name: diphenhydramine
0 reviewsAdd rating
Dimetapp Children's ND Non-Drowsy Allergy (Pro)
Generic name: loratadine
0 reviewsAdd rating
Diphedryl
Generic name: diphenhydramine
0 reviewsAdd rating
Diphen
Generic name: diphenhydramine
0 reviewsAdd rating
Dytuss
Generic name: diphenhydramine
0 reviewsAdd rating
Ed-Chlortan
Generic name: chlorpheniramine
0 reviewsAdd rating
Ed ChlorPed
Generic name: chlorpheniramine
0 reviewsAdd rating
Ed Chlor Ped Jr.
Generic name: chlorpheniramine
0 reviewsAdd rating
Histex
Generic name: triprolidine
0 reviewsAdd rating
Histex CT
Generic name: carbinoxamine
0 reviewsAdd rating
Histex IE
Generic name: carbinoxamine
0 reviewsAdd rating
Histex PD
Generic name: carbinoxamine
0 reviewsAdd rating
Karbinal ER (Pro)
Generic name: carbinoxamine
0 reviewsAdd rating
Leader Allerhist
Generic name: clemastine
0 reviewsAdd rating
M-Hist PD
Generic name: triprolidine
0 reviewsAdd rating
ohm Allergy Relief
Generic name: loratadine
0 reviewsAdd rating
PediaTan
Generic name: chlorpheniramine
0 reviewsAdd rating
Pediatex
Generic name: carbinoxamine
0 reviewsAdd rating
Pediox
Generic name: carbinoxamine
0 reviewsAdd rating
Polmon
Generic name: dexchlorpheniramine
0 reviewsAdd rating
Quzyttir (Pro)
Generic name: cetirizine
0 reviewsAdd rating
Ryclora (Pro)
Generic name: dexchlorpheniramine
0 reviewsAdd rating
Ryvent (Pro)
Generic name: carbinoxamine
0 reviewsAdd rating
Scot-Tussin Allergy
Generic name: diphenhydramine
0 reviewsAdd rating
Siladryl Allergy
Generic name: diphenhydramine
0 reviewsAdd rating
Siltane
Generic name: brompheniramine
0 reviewsAdd rating
Tavist Allergy
Generic name: clemastine
0 reviewsAdd rating
Tavist ND
Generic name: loratadine
0 reviewsAdd rating
Topco Allergy
Generic name: chlorpheniramine
0 reviewsAdd rating
Tripohist
Generic name: triprolidine
0 reviewsAdd rating
Twilite
Generic name: diphenhydramine
0 reviewsAdd rating
Valu-Dryl
Generic name: diphenhydramine
0 reviewsAdd rating
Vanaclear PD
Generic name: triprolidine
0 reviewsAdd rating
Vanahist PD
Generic name: triprolidine
0 reviewsAdd rating
Vicks QlearQuil All Day & All Night 24 Hour Allergy Relief
Generic name: loratadine
0 reviewsAdd rating
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.