Promethazine is widely used in the medical field primarily as an antihistamine to treat allergic reactions such as hay fever, hives, and conjunctivitis. It is also effective in managing nausea and vomiting, particularly post-operative nausea or that induced by motion sickness. Additionally, it serves as a sedative to help with anxiety or as a sleep aid due to its calming effects on the central nervous system. In some cases, it is used as an adjunct to analgesics for pain relief, enhancing the effects of painkillers. Its antiemetic and sedative properties make it a versatile medication in both hospital and outpatient settings.