Claritin (loratadine) is a long-acting, non-sedating antihistamine that is used to treat symptoms of non-nasal and nasal seasonal allergic rhinitis and hives. 

Histamine is a chemical that causes many of the signs and symptoms of an allergy. Histamine is released from histamine-storing cells (mast cells) and attaches to other cells that have receptors for histamine on their surfaces. Histamine stimulates the cells to release chemicals that produce effects that we associate with allergy, including welts, itching, and tissue swelling. 

Loratadine blocks one type of histamine receptor (the H1 receptor) and thus prevents activation of cells with H1 receptors by histamine. Unlike some antihistamines, loratadine does not enter the brain from the blood and, therefore, does not cause drowsiness when taken at recommended doses. 

Common side effects of Claritin include

• headache,
• drowsiness,
• fatigue,
• dry mouth,
• nervousness, and
• difficulty sleeping.

Serious side effects of Claritin include

• fast or uneven heart rate,
• severe headache, and
• lightheadedness.

Drug interactions of Claritin include erythromycin, cimetidine, and ketoconazole, because they increase the blood concentration of Claritin by inhibiting the elimination of Claritin. This may result in increased adverse events from Claritin. 

St. John's wort, carbamazepine, and rifampin reduce blood levels of Claritin. 

Claritin is not expected to harm a fetus. Tell your doctor if you are pregnant or plan to become pregnant. 

Claritin is secreted in breast milk at levels similar to blood levels. Nursing mothers should decide whether to stop breastfeeding or discontinue Claritin.

The most common adverse events with loratadine are:

• headache,
• drowsiness,
• fatigue and
• dry mouth.

Nervousness and difficulty sleeping have also been reported.

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