The active ingredient in Claritin is loratadine, an antihistamine that reduces sneezing, itching and runny nose that result from allergies, according to Drugs.com. There are 10 milligrams of loratadine in each Claritin tablet. Claritin-D contains the active ingredient pseudoephedrine, a decongestant, along with loratadine, according to Bayer.
The inactive ingredients in Claritin include corn starch, lactose monohydrate and magnesium stearate, Drugs.com details. The corn starch is a derivative of corn, and the lactose monohydrate is derived from cow's milk, according to Bayer. The latter is a milk sugar that helps form the pill shape, while corn starch helps the pill break down for absorption, Drugs.com details.