Background Diphenhydramine is a first-generation H1 receptor antihistamine that is usually used for the treatment of allergy, insect bites such as mosquitos, bee stings, and some types of skin rashes. However, it possesses antiparkinsonian, antitussive, antiemetic, and most importantly hypnotic properties. This study aimed to assess the prevalence, frequency of use, and dosage of over-the-counter (OTC) sleep aid containing diphenhydramine hydrochloride used among Saudis. Material and Methods The study used a descriptive cross-sectional design conducted among the Saudi population. An online self-administered questionnaire was distributed among the selected Saudi nationality using social media platforms. The subjects included were Saudis aged 15 years or older, literate in using social media. The questionnaire included basic demographic characteristics, previous and current history of medication use that contains diphenhydramine hydrochloride, its side effects, and other related behavior of using, such as frequency of use and dosage. Results A total of 414 respondents were recruited (51% males and 49% females). Previous and current use of medications that contain diphenhydramine hydrochloride constituted 87.2% and 31.9%, respectively. The most common reason for using sleep aid was insomnia (52.1%). Dizziness or imbalance was the most commonly reported side effect. The Chi-square test revealed that the age group of ≤25 years (p = 0.044), female gender (p = 0.040), being a student (p = 0.015), current use of sleeping aid medications (p < 0.001), and the use of other medications (p < 0.001) were significantly associated with increased use of sleep aid medications. Conclusion The excessive use of over-the-counter (OTC) sleep aid medications containing diphenhydramine hydrochloride was widely prevalent among the Saudi population. Younger female students constitute the majority of OTC sleep aid medication users.