It is easy to get buried in the drug avalanche, unable to distinguish the side effects of antihistamines like Claritin and Allegra.

A side effect of antihistamines is somnolence, and it is therefore recommended not to take these drugs while driving an automobile or during the consumption of alcoholic beverages.

Children may be more sensitive to the effects of antihistamines.

Infants are especially sensitive to the effects of antihistamines, and serious side effects could occur in a nursing baby.

An effect of antihistamines is to thicken mucus secretions.

Caution is advised when using this drug in children because they are more sensitive to the effects of antihistamines.

The opioid-potentiating effects of other antihistamines such as hydroxyzine, cyclizine etc. appear to be directly due to additive sedation, and promethazine also has metabolic effects on codeine and the like, namely increasing the percentage of codeine that the liver converts to morphine in most people.

Note: Women who breast-feed should avoid them, as should the elderly, who sometimes are more sensitive to the effects of antihistamines.