Diphenhydramine's trade name is Benadryl. It is a very potent antihistamine that crosses the blood brain barrier, which is why it makes you sleepy, be careful with it. One of the lesser known side effects is that it impairs transfer of short term memory to long term memory, causing some people to forget things like where their car is parked, where they are going after starting on a trip, etc.
It is a great allergy med, but be aware of the side effects, like all meds, they can be more than you expect.
Claritin is less potent at the nonprescription level, but much less sedating. Allegra is more potent at presription strength than non-prescription strength Claritin. It is probably the only truly non-sedating antihistamine out there, prescription or otherwise.
However, ANY medicine can have unexpected side effects in any given individual, so some people can get sleepy on supposdedly non-sedating meds, and others can get wired on meds that should make them sleepy.
The nasal steroids, like Flonase, work very well in most people, but Americans seem to dislike nasal sprays as a rule and don't stay on them long enough to get good long term symptom relief. We want to be better, TODAY, dang it!!!
Sudafed is Pseudoephedrine, a decongestant, and works well fast to relieve symptoms, but does not help the cause. It can raise blood pressure, cause, dry mouth, etc.
Bill