What is the most common OTC medication used to treat insomnia?

The most common over-the-counter (OTC) medication used to treat insomnia is diphenhydramine, an antihistamine found in products like Benadryl and Nytol. Another popular option is doxylamine, which is also an antihistamine and can be found in brands like Unisom. While these medications may help with sleep onset, they can cause side effects such as drowsiness the next day and are not recommended for long-term use. It's advisable to consult a healthcare professional before using them for insomnia.