What are some over-the-counter medications to treat anxiety?
First generation antihistamines in some cases can help. And a various assortments of natural supplements.
First Generation Anti-Histamines
Promethazine (Dependent on the country, in the USA this is Rx only)
Hydroxyzine (See above)
GABA (Gamma-Aminobutyric Acid)
(Note: This is not by all means an extensive list of all OTC medications/supplements)