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A member asked:
What is the difference between first and second-generation antihistamines?
5 doctors weighed in across 3 answers
Side effects: The second generation antihistamines were developed to try and decrease the side effects of the first generations. Many are "purified" first generation antihistamines so they have the active effects without the side effects of drowsiness, sedation, dry mouth etc. They also tend to have longer half lives, meaning they can be taken once or twice a day not every 4 hours.
Answered 1/28/2019
6.4k views
Antihistamines: 1st generation are better antihistamines but have significant drowsiness. 2nd generation do not bind the receptor as well as 1st generation, but they cause much less drowsiness.
Answered 9/1/2018
5.5k views
Sleepyness: The first generation antihistamines (benadryl, chlor-trimeton, tavist) are short acting and usually make people sleepy. Second generation (claritin, zyrtec, allegra, xyzal, (levocetirizine) clarinex) are long acting once a day, and generally do not make people sleepy, or less so.
Answered 1/28/2019
5.5k views
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