Aloin also called barbaloin, is a bitter, yellow-brown colored compound. Barbaloin, a secondary phenolic metabolite, is distributed in the plants as part of a peripheral defence strategy. Barbaloin content was found to be highest in the youngest leaves.

Aloin extracted from natural sources is a mixture of two diastereomers, termed Aloin A (also called barbaloin) and Aloin B (or isobarbaloin). Aloin is usually prepared by extraction from aloe latex, the bitter yellow exudate that seeps out from just underneath the skin of aloe leaves. The latex is then dried and powdered to make the final product, often made into tablets or a beverage, though aloin does not have good stability in aqueous solutions. Products derived from the gel of the aloe plant do not contain appreciable amounts of aloin, and have not been proven effective for any disease or condition when taken orally