1. First-Generation Antihistamine
This is an older class of antihistamine, developed before newer, second-generation versions.
They’re effective at blocking H1 histamine receptors, which helps reduce allergy symptoms; however, this medicine can cross the blood-brain barrier, which means it can leave you feeling drowsy and less alert.
Like with all antihistamines, side effects are possible. These include:
- Dry mouth
- Increased heart rate
- Constipation
- Trouble urinating
- Dizziness
- Blurry vision
- Headaches
- Mucous thickening
- Lowered blood pressure
First-generation antihistamines work fast and are effective for short-term symptom relief. Aside from allergies, they’re also used for:
- Motion sickness and nausea
- Insomnia
- Anxiety (in some cases)
- Itching and skin reactions
If you need to stay alert, this may not be the best option as a daily antihistamine. They can also interact with alcohol and other sedatives.
2. Second-Generation Antihistamine
Second-generation antihistamines are a newer class of allergy medications designed to relieve symptoms without causing drowsiness. They are usually referred to as a non-drowsy antihistamine.
Just like first-generation antihistamines, they block H1 histamine receptors, but don’t easily cross the blood-brain barrier, making them ideal for daytime use.
They treat a range of allergies, including:
- Hay fever
- Hives
- Food allergies
- Dust mites
- Tree pollen
- Insect bites
- Skin rashes
- Reactions to medications
These antihistamines can be a good option for consistent and preventative management as they’re safe for treating chronic allergies.
Some of the reported side effects include:
- Headache
- Nausea
- Vomiting
- Coughing
- Sore throat
- Abdominal pain
- Fatigue
Side effects are typically mild; however, some second-generation antihistamines can cause drowsiness.
If you also need to treat non-allergic symptoms, such as motion sickness or insomnia, a first-generation antihistamine may be better suited.
