Phenergan 10mg tablets are taken to treat allergic conditions such as hayfever rashes or hives or to prevent travel sickness also to treat adults with difficulty sleeping insomniafor allergic conditions eg hayfeverchildren 510 years either a single dose of 1 or 2 tablets at night or 1 tablet twice daily total dose must not exceed 2 tablets per daychildren over 10 years old and adults start with one tablet twice a day this may be increased to two tablets three times a day if necessaryfor