Promethazine hydrochloride is a phenothiazine drug used to treat a variety of conditions that range from allergies, colds, nausea, and vomiting to sedation and motion sickness. It can also be used to reduce the amount of coughing a person experiences. Promethazine hydrochloride is most commonly found in combination with other medications, but it is available in tablet and syrup form on its own. The most common side effects of promethazine hydrochloride include dry mouth, drowsiness, headaches, nervousness, and difficulty sleeping. Other more serious side effects may include an irregular heartbeat, difficulty breathing, chest pain, and seizure. People taking promethazine hydrochloride are cautioned to avoid drinking alcohol, driving, or operating heavy machinery, as the drug can cause dizziness and drowsiness. Promethazine hydrochloride is mainly used to treat symptoms of colds and allergies, but it may be prescribed by a doctor to treat nausea and vomiting, motion sickness, sedation, or preoperative sedation. It’s also used to treat and prevent the symptoms of opioid withdrawal. It should always be taken as prescribed by a doctor. Promethazine hydrochloride is a useful and effective drug when taken correctly, however it must be used with caution. Patients should discuss potential side effects, interactions, and other safety information with their doctor before taking promethazine hydrochloride.