Plenadren is a medication designed for the treatment of adrenal insufficiency, a condition where the adrenal glands do not produce adequate amounts of certain hormones, primarily cortisol. It contains hydrocortisone as its active ingredient, which is a synthetic version of cortisol. Plenadren is formulated as a modified-release tablet, allowing for a once-daily oral administration that mimics the body's natural rhythm of cortisol production more closely than immediate-release hydrocortisone formulations. This innovative delivery system helps to improve the quality of life for patients by providing a more physiological replacement therapy, aiming to reduce the risk of both under- and over-replacement symptoms. It is used in adults for the treatment of adrenal insufficiency and may not be suitable for all patients, including those with certain medical conditions or who are taking specific medications.