Active ingredients include pseudoephedrine and phenylpropanolamine. Sometimes, young children can have an opposite reaction, and get very drowsy after taking them. Antihistamines are used to help improve a runny nose, however medical evidence shows that while they are definitely helpful in stopping a runny nose caused by allergies, they are not particularly useful in stopping a runny nose caused by a cold. Active ingredients include chlorpheniramine, bromopheniramine, and diphenhydramine. The major side effect of this class of drugs is sedation.
Many people get very sleepy after taking antihistamines.
Young children sometimes have an opposite reaction and get very excited after taking them. Cough suppressants decrease the frequency and intensity of a cough. They work by telling your brain not to cough as much. When used in excess, they can cause sedation, but have minimal side effects if used in normal doses. The most common active ingredient in cough suppressants is dextromethorphan.