Does Benadryl Work Faster than Zyrtec?

Benadryl and Zyrtec can both begin relieving allergy symptoms within about an hour, although the timing varies by person. Benadryl (diphenhydramine) may start working somewhat sooner for some people, but the stated times to peak or full effectiveness do not establish that it is consistently faster than Zyrtec (cetirizine). However, Zyrtec provides longer-lasting relief, working for up to 24 hours compared to Benadryl's 4-6 hour duration. Benadryl is more likely to cause drowsiness because it enters the brain more readily. Zyrtec is less sedating for many people, but it can still cause drowsiness. For longer-lasting daily allergy relief, a less-sedating antihistamine such as Zyrtec is often preferred.