Chlo Hist is a combination medication containing chlophedianol (a cough suppressant) and dexbrompheniramine (an antihistamine). It can be taken by adults and children to help with certain allergy and common cold symptoms, such as cough, runny nose, and itchy eyes. Chlo Hist (chlophedianol / dexbrompheniramine) is taken by mouth, typically every 6 hours, as needed. It's available as a brand name oral solution (liquid) that you can buy over the counter. Some side effects of this medication include include dizziness and sleepiness