What are Antihistamines?

What are Antihistamines?

Antihistamines are a type of medication used to treat the symptoms of allergies. Some antihistamines can also be used to treat travel (motion) sickness and as a short-term sleep remedy. 

Antihistamines fall into two main categories:

  •  H1 blockers which are used to treat the symptoms of allergies and motion sickness 
  • H2 blockers which are used to treat conditions affecting your stomach and digestive tract including acid reflux, stomach ulcers, and nausea. 

This article will focus on H1 blockers and the treatment of allergy symptoms. 

H1 blockers fall into two further groups. The older antihistamines, known as first-generation antihistamines, have the effect of making you sleepy or drowsy after taking them. Newer, second-generation antihistamines (also known as non-drowsy antihistamines) are less likely to make you sleepy. 

First-generation antihistamines include cinnarizine, promethazine, chlorphenamine, hydroxyzine, and diphenhydramine. Second generation antihistamines include fexofenadine, loratadine, acrivastine and cetirizine. 

Many antihistamines can be bought over the counter, but you will need a prescription for stronger ones. Antihistamines are available as tablets, nasal sprays, capsules, liquids, eye drops, and topical gels and lotions.