Final answer:
Antihistamines used as cough suppressants can cause mild sedation and reduce other symptoms for allergic rhinitis. However, they are not recommended for chronic or non-specific cough, especially in young children. Long-term use of diphenhydramine may have negative effects in older individuals.
Step-by-step explanation:
Antihistamines that work as cough suppressants can have various side effects. These may include mild sedation, as well as a reduction in other associated symptoms like a runny nose and watery eyes for allergic rhinitis. However, antihistamines are not recommended as an empirical therapy for chronic or non-specific cough, especially in very young children. Long-term use of diphenhydramine, a type of antihistamine, has been associated with negative outcomes in older people.