Which medication is typically used for seasonal allergies and has a common side effect of dry mouth?

Diphenhydramine HCL is an antihistamine commonly used to relieve symptoms associated with seasonal allergies, such as sneezing, runny nose, and itching. One of the well-known side effects of diphenhydramine is dry mouth, which occurs because antihistamines block histamine receptors that also play a role in regulating saliva production. This can lead to decreased saliva flow and the resulting sensation of a dry mouth.

The other medications listed do not typically have this side effect or are not indicated for treating seasonal allergies. For example, penicillin is an antibiotic used to treat bacterial infections, tolnaftate is an antifungal medication used for treating skin infections, and atenolol is a beta-blocker used primarily for managing blood pressure and heart conditions. None of these are indicated for allergy relief nor are they associated with dry mouth as a common side effect.