The most common side effect of Claritin is head pain, according to WebMD. Less common side effects include drowsiness and pink eye, and adults and children over the age of 12 may experience dry mouth, fatigue and drowsiness, according to Drugs.com.
Additional side effects of Claritin may include high blood pressure, heart palpitations, low blood pressure, syncope and a rapid heart beat, states Drugs.com. Rarely, a person may experience side effects such as blurred vision, having trouble sleeping, dryness of the nose, ringing in the ears and trouble breathing, states WebMD. Those who discover large hives or have an allergic reaction should seek medical help.