Phenergen DM syrup is a medication typically used to treat symptoms such as a runny nose, coughing and sneezing that are caused by allergies or a cold. It contains the active ingredient promethazine, which is an antihistamine that works by blocking the effects of histamines, compounds that the body releases when exposed to allergens. The other active ingredient in Phenergen DM is dextromethorphan, a cough suppressant.
Phenergen DM syrup is available only by prescription in the United States. The typical dose is one teaspoon or 5 milliliters. The medication is absorbed rapidly by the digestive system and begins relieving symptoms within 15 to 30 minutes, with the effects typically lasting between three and six hours.
Phenergen DM syrup should not be used by patients who are taking monoamine oxidase inhibitor medications or those who suffer from asthma or COPD. It is not recommended for patients under the age of 2 because of the high risk of respiratory distress in these young patients. Most adults and children over the age of 2 respond well to Phenergen DM syrup, but some do experience side effects such as dizziness, lightheadedness or dry mouth. In many cases, taking a lower dose eases these side effects. Severe side effects, such as decreased coordination and blurry vision, are rare.