It is safe to give, we prescribe it (diphenhydramine hcl) for our patients pretty frequently for allergies and allergic reactions and such. But, First, why do you feel he needs it and second, if you do give it make sure it ONLY contains diphenhydramine and NOT any other ingredients such as any decongestant or acetaminophen (Tylenol) or ibuprofen, etc.
As the pattern continues, consult a vet. There are free "ask-a-vet," or something similar numbers you can find. Another way to have your pooch feel better, is call a vet that does charge and ask the receptionist. Chances are, they will know. If they don't, most vets will answer a question like this over the phone. Good luck and I hope your pooch feels better. Happy Holidays!
lf you're concerned about calming an anxious dog, get a bottle of Rescue Remedy. lt's especially for this purpose, l give it to my cats whenever we travel. Rescue Remedy is available at most pet supply stores.