Mefloquine hydrochloride is primarily used as an antimalarial medication, particularly for the prevention and treatment of malaria caused by Plasmodium falciparum and Plasmodium vivax. It is often prescribed for travelers visiting regions where malaria is endemic, as it provides long-lasting protection with a weekly dosage. The drug is effective against chloroquine-resistant strains of malaria, making it a valuable option in areas where resistance is a concern. Additionally, it is sometimes used in combination with other antimalarial agents to enhance efficacy or reduce the risk of resistance development. Beyond malaria, mefloquine hydrochloride has been explored for its potential use in treating certain autoimmune diseases and psychiatric conditions, though these applications are less common and require further research. Due to its potential side effects, including neuropsychiatric symptoms, it is typically reserved for individuals who cannot tolerate or have contraindications to other antimalarial drugs.