Antihistamines are often advised for the treatment of allergies, which are found in over-the-counter (OTC) allergy medications, sleep medications, and cold or flu medicines. They help treat allergy symptoms such as sneezing, runny or stuffy nose, nasal congestion, skin rashes, hives, and itching.

We all know the brands – Zyrtec, Claritin, Allegra, Benadryl, and Atarax. There are different types of antihistamines, which are classified as first generation, second generation, and third generation antihistamines. First generation antihistamines are the older ones, while the second and third generation antihistamines are the newer ones.

Irrespective of the generation, all antihistamines have the same action mechanism. They work by inhibiting the secretion and effects of histamine, a substance that our body produces when an allergic reaction takes place. Histamine is produced when our immune system fights an allergen, causing symptoms such as sneezing, congestion, and itching.

Before understating the difference between first, second, and third generation antihistamines, it is important to know what they are.

First Generation Antihistamines

Older generation antihistamines have been there for over 60 years. Undeniably, they are effective but they are known to have sedating effects.

One of the most well-known brands is diphenhydramine (Benadryl), which is often found in OTC allergy meds, sleep medications, cough, and cold preparations. It is also found in certain medications along with pain relievers like paracetamol and ibuprofen. Cyproheptadine (Periactin), chlorpheniramine (Chlor-Trimeton), and doxylamine (Unisom) are a few other drugs that belong to the first generation antihistamines.

Second and Third Generation Antihistamines

These newer antihistamines are also effective at treating allergies but unlike older ones, they are known to cause less drowsiness. Second generation antihistamines include cetirizine (Zyrtec) and loratadine (Claritin). Third generation antihistamines include fexofenadine (Allegra). They are available over the counter.

So, what is the difference? As mentioned earlier, older ones have more sedative effects than the newer ones.

First generation antihistamines are to be taken four to six times a day for a certain period of time, while the newer ones need to be taken once or twice a daily.

People suffering from seasonal allergies can use OTC antihistamines such as Zyrtec, Claritin, and Allegra without visiting a doctor. If one does not get relief from these medications, they should seek medical attention for further evaluation.

Older people should take first generation antihistamines with extra caution because of their sedative properties. Ideally, they should consult with a doctor. Older antihistamines have been associated with accidental falls, especially in older individuals. In some people above 65 years, older histamines can cause urinary troubles because the drugs work by decreasing bodily fluids, including urine.

For more information on the difference between first, second, and third generation antihistamines, please check with your primary care physician.