Dicelgis does cause drowsiness and should not be taken if you are allergic to doxylamine or pyridoxine, or to
other antihistamines such as Benadryl or Dramamine.
Zyrtec is a second generation drug, which means that it does not cause sedation
like other antihistamine medications, like Benadryl.
One advantage that it has
over other antihistamines is that it usually doesn't have the side effect of drowsiness often associated with similar medications.
Often Zyrtec will be tried only
after other antihistamines, such as Benadryl, have failed to arrest the symptoms of allergy related Dermatitis.
While you can take Benadryl or
other antihistamines, you'll find that they will make you tired.
That's because it and
other antihistamines have a sedating effect.
Can I administer Benadryl or
other antihistamines?
Do not use in an animal with an allergy to diphenhydramine or
other antihistamines.
If your dog is suffering an allergic reaction from flea bites or he's just really miserable and nothing else is working, you can give him Benadryl or
any other antihistamine to reduce itchiness, swelling and pain.
(ref)
Other antihistamines have not proved very helpful for asthmatic cats.
Tell your veterinarian if your pet is allergic to diphenhydramine or
other antihistamines.