Isotretinoin is a retinoid that is widely used in the treatment of severe (often disfiguring) nodular acne, primarily in adolescents. Although the exact mechanism of action is unknown, isotretinoin acts by inhibition of sebaceous gland function and keratinization. This retinoic acid derivative is also used to treat other skin diseases, although it is known to cause birth defects in humans and should be used with extreme caution (preferably not at all) during pregnancy. Side effects are not common, but include chest pain, dizziness, fast heartbeat (more common for injection), and skin rash.