If i took an allegra at 11am, can i take benadryl (diphenhydramine) 12 hours later?

Benadryl (diphenhydramine): The main risk of taking Benadryl (diphenhydramine) with the "non"sedating antihistamines in creating some drowsiness. The closer together the increase likelihood for having drowsiness.

Yes: Benedryl has some benefits as a really tenacious antihistamine that binds well with histamine & is very effective in that work.Its drawback is sedation which occurs because it enters the brain & messes with messages between nerve cells. You can take benedryl along with a non-sedating antihistamine as long as you can handle the side effects.