Phenergan tablets 25 mg is a phenothiazine antihistamine it works by blocking the site of histamine acts in the bodyphenergan tablets 25 mg may be used for the following purposesto treat allergic conditions such as hay fever or rashes like nettle rash or hivesto treat adults with difficulty sleeping insomniato prevent or control nausea and vomiting during and after surgeryto help promote light sleepprevent motion sicknesshow to takechildren 510 years maximum 1 tablet at nightchildren over 10 y